MAILSEND-GO(1)

Introduction
mailsend-go (https://github.com/muquit/mailsend-go) is a command line tool to send mail via SMTP protocol. This is the golang (https://golang.org/) incarnation of my C version of mailsend (https://github.com/muquit/mailsend/) . However, this version is much simpler and all the heavy lifting is done by the package gomail.v2 (https://gopkg.in/gomail.v2) However, this package is not maintained anymore. Therefore, I forked it to gomail (https://github.com/muquit/gomail) (starting from mailsend-go v1.0.11-b1 Aug-24-2025). The main purpose of this fork is to add XOAUTH2 (https://developers.google.com/workspace/gmail/imap/xoauth2-protocol) support (Bug #68) but it also contains a security fix to prevent STARTTLS downgrade attack.

If you use mailsend (https://github.com/muquit/mailsend/) , please consider using mailsend-go as no new features will be added to mailsend (https://github.com/muquit/mailsend/) .

If you have any question, request or suggestion, please enter it in the Issues (https://github.com/muquit/mailsend-go/issues) with appropriate label.

NOTE: XOAUTH2 support was added in v1.0.11-b1 (Released on Aug-24-2025)

Please look at ChangeLog for what has changed in the current version.

XOAUTH2 support
XOAUTH2 (https://developers.google.com/workspace/gmail/imap/xoauth2-protocol) support is available in v1.0.11-b1 (Released on Aug-24-2025). mailsend-go (https://github.com/muquit/mailsend-go) itself does not implement full OAuth2 flow because implementing full OAuth2 would require managing web browser redirects, secure token storage across different platforms and maintaing state of token refresh cycles.

Therefore, I’ve created a companion tool called oauth-helper (https://github.com/muquit/oauth-helper) for token management. This separation keeps mailsend-go (https://github.com/muquit/mailsend-go) simple and secure while giving you full control over how tokens are obtained and stored. For automation, just pipe token from oauth-helper (https://github.com/muquit/oauth-helper) directly into mailsend-go (https://github.com/muquit/mailsend-go) .

Please visit oauth-helper (https://github.com/muquit/oauth-helper) page for details. It has examples on how to integrate with mailsend-go (https://github.com/muquit/mailsend-go) and XOAUTH2 (https://developers.google.com/workspace/gmail/imap/xoauth2-protocol) .

Please create an Issues (https://github.com/muquit/mailsend-go/issues) if you need help or have any questions.

Features

•   Add a mail body

•   Support Multiple Attachments

•   Supports ESMTP Authentication

•   Supports StartTLS and SSL

•   Send mail to a list of users

•   Show SMTP server info etc.

Contributing
Please send a pull request if you add features, fix bugs or update the documentation.

If you want to update the documentation, please do not update README.md directly, rather update the Markdown files in docs/ directory. README.md is generated by markdown-toc-go (https://github.com/muquit/markdown-toc-go) assembling the individual Markdown files in the docs/ directory. If you would like to generate README.md, type make gen (you will need required tools of course)

Synopsis

         Version: @($) mailsend-go v1.0.12
         https://github.com/muquit/mailsend-go
         Compiled with go version: go1.26.3
         mailsend-go [options]
          Where the options are:
          -debug                 - Print debug messages
          -sub subject           - Subject
          -t to,to..*            - email address/es of the recipient/s. Required
          -list file             - file with list of email addresses.
                                   Syntax is: Name, email_address
          -fname name            - name of sender
          -f address*            - email address of the sender. Required
          -cc cc,cc..            - carbon copy addresses
          -bcc bcc,bcc..         - blind carbon copy addresses
          -rt rt                 - reply to address
          -smtp host/IP          - hostname/IP address of the SMTP server. Required
                                   unless '-use' is set.
          -use mailprovider      - Arranges -smtp, -port and -ssl for you when using
                                   a well known mailprovider. Allowed values:
                                   gmail, yahoo, outlook, gmx, zoho, aol
          -port port             - port of SMTP server. Default is 587
          -domain domain         - domain name for SMTP HELO. Default is localhost
          -info                  - Print info about SMTP server and exit
          -printCerts            - Print Certificates in connection with -info. Default is No
          -ssl                   - SMTP over SSL. Default is StartTLS
          -verifyCert            - Verify Certificate in connection. Default is No
          -ex                    - show examples
          -help                  - show this help
          -q                     - quiet
          -log filePath          - write log messages to this file
          -cs charset            - Character set for text/HTML. Default is utf-8
          -V                     - show version and exit
          auth                   - Auth Command
           -user username*       - For basic auth: username for ESMTP authentication
                                   For OAuth2: email address of the authenticated account
                                   Required for both auth methods
           -pass password*       - password for ESMTP authentication. Required for basic auth
           -oauth2               - Use OAuth2 XOAUTH2 authentication instead of basic auth
           -token access_token*  - OAuth2 access token. Required when -oauth2 is used
          body                   - body command for attachment for mail body
           -msg msg              - message to show as body
           -file path            - or path of a text/HTML file
           -mime-type type       - MIME type of the body content. Default is detected
          attach                 - attach command. Repeat for multiple attachments
           -file path*           - path of the attachment. Required
           -name name            - name of the attachment. Default is filename
           -mime-type type       - MIME-Type of the attachment. Default is detected
           -inline               - Set Content-Disposition to "inline".
                                   Default is "attachment"
          header                 - Header Command. Repeat for multiple headers
           -name header          - Header name
           -value value          - Header value
        The options with * are required.
        Environment variables:
           SMTP_USER_PASS for auth password (-pass)
           SMTP_OAUTH_TOKEN for OAuth2 access token (-token)
        XOAUTH2 helper:
           Please visit the following link for a tool to help obtain
           OAuth2 access token for mailsend-go:
             https://github.com/muquit/oauth-helper

Vulnerability Check

        ➤ govulncheck --version
        Go: go1.26.3
        Scanner: govulncheck@v1.3.1-0.20260508232743-57fb27ec3243
        DB: https://vuln.go.dev
        DB updated: 2026-05-07 19:21:40 +0000 UTC

        ➤ govulncheck -show verbose ./...
        Fetching vulnerabilities from the database...
        Checking the code against the vulnerabilities...
        The package pattern matched the following 2 root packages:
          github.com/muquit/mailsend-go/pkg/version
          github.com/muquit/mailsend-go
        Govulncheck scanned the following 2 modules and the go1.26.3 standard library:
          github.com/muquit/mailsend-go
          github.com/muquit/gomail@v1.0.2
        No vulnerabilities found.

updated: Ma | y-16-2026 | 16-2026) ion of m | ailsend-go is 1.0.12, released on May-16-2026.
1084 33880 5563904 34185 903 | 01-16-2026 01-16-2026 01-16-2026 01-16-2026 01-16-2026 | 20:10 20:10 20:10 20:10 20:10 | mailsend-go-v1.0.11-windows-amd64.d/LICENSE.txt mailsend-go-v1.0.11-windows-amd64.d/README.md mailsend-go-v1.0.11-windows-amd64.d/mailsend-go-v1.0.11-windows-amd64.exe mailsend-go-v1.0.11-windows-amd64.d/mailsend-go.1 mailsend-go-v1.0.11-windows-amd64.d/platforms.txt

5633956 5 files

        After extracting the archive, copy the binary somewhere in your PATH.
        Example:
        ```bash
        sudo /bin/cp -fv \
                 mailsend-go-v1.0.11-linux-amd64.d/mailsend-go-v1.0.11-linux-amd64 \
                 /usr/local/bin/mailsend-go
        sudo /bin/cp -fv \
                 mailsend-go-v1.0.11-linux-amd64.d/mailsend-go.1 \
                 /usr/share/main/man1

  Installing using Scoop on Windows
If you don’t have Scoop installed, run in PowerShell:

        Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser
        Invoke-RestMethod -Uri https://get.scoop.sh | Invoke-Expression

For more information, see https://scoop.sh

•   Install

        scoop install mailsend-go

•   Update

        scoop update mailsend-go

•   Remove

        scoop uninstall mailsend-go

•   Misc

        scoop list
        scoop status
        scoop info mailsend-go
        scoop cat mailsend-go

  Installing using Winget on Windows
You can install mailsend-go with Winget (https://learn.microsoft.com/windows/package-manager/winget/) on Windows:

        winget install muquit.mailsend-go

  Installing using Homebrew on Mac
You will need to install Homebrew (https://brew.sh/) first. Note: Homebrew (https://brew.sh/) formula will be avilable only for released versions of mailsend-go

  Installing
First install the custom tap.

        brew tap muquit/formulae
        brew install mailsend-go

Or use auto-tap (installs in one command):

        brew install muquit/formulae/mailsend-go

Note: If you previously used the old dedicated tap (muquit/mailsend-go), you may get an ambiguity error. Migrate to the new tap with:

        brew uninstall mailsend-go
        brew untap muquit/mailsend-go
        brew install muquit/formulae/mailsend-go

  Updating

        brew upgrade mailsend-go

  Uninstalling

        brew uninstall mailsend-go

To remove the tap:

        brew untap muquit/formulae

Compiling from source
Requires the Go programming language toolchain (https://golang.org/dl/) and git. mailsend-go uses Go modules (https://github.com/golang/go/wiki/Modules) for dependency management.

To install the binary:

        $ go install github.com/muquit/mailsend-go@latest

The binary will be installed in $GOPATH/bin/.

To compile yourself:

        $ git clone https://github.com/muquit/mailsend-go.git
        $ cd mailsend-go
        $ go build .

Or for platform-specific builds:

        $ make linux
        $ make mac
        $ make windows

Run make help for all available targets.

To list the packages used:

        $ go list -m "all"
        github.com/muquit/mailsend-go
        github.com/muquit/gomail v1.0.2
        github.com/muquit/quotedprintable v0.0.0-20250204043250-71206103869d

Examples
Each example mailsend-go command is a single line. In Unix back slash can be used to continue in the next line. Also in Unix, use single quotes instead of double quotes, otherwise if input has any shell character like $ etc, it will get expanded by the shell. The directory test/ has some test scripts.

  Show SMTP server information

  StartTLS will be used if server supports it

          mailsend-go -info -smtp smtp.gmail.com -port 587

        [S] 220 smtp.gmail.com ESMTP k185-v6sm17739711qkd.27 - gsmtp
        [C] HELO localhost
        [C] EHLO localhost
        [S] 250-smtp.gmail.com at your service, [x.x.x.x]
        [S] 250-SIZE 35882577
        [S] 250-8BITMIME
        [S] 250-STARTTLS
        [S] 250-ENHANCEDSTATUSCODES
        [S] 250-PIPELINING
        [S] 250-CHUNKING
        [S] 250-SMTPUTF8
        [C] STARTTLS
        [S] 220-2.0.0 Ready to start TLS
        [C] EHLO localhost
        [S] 250-smtp.gmail.com at your service, [x.x.x.x]
        [S] 250-SIZE 35882577
        [S] 250-8BITMIME
        [S] 250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH
        [S] 250-ENHANCEDSTATUSCODES
        [S] 250-PIPELINING
        [S] 250-CHUNKING
        [S] 250-SMTPUTF8
        Certificate of smtp.gmail.com:
         Version: 3 (0x3)
         Serial Number: 149685795415515161014990164765 (0x1e3a9301cfc7206383f9a531d)
         Signature Algorithm: SHA256-RSA
         Subject: CN=Google Internet Authority G3,O=Google Trust Services,C=US
         Issuer: GlobalSign
         Not before: 2017-06-15 00:00:42 +0000 UTC
         Not after: 2021-12-15 00:00:42 +0000 UTC
        [C] QUIT
        [S] 221-2.0.0 closing connection k185-v6sm17739711qkd.27 - gsmtp

  Use SSL. Note the port is different

          mailsend-go -info -smtp smtp.gmail.com -port 465 -ssl

  Print SMTP server certificate chain

          mailsend-go -info -smtp smtp.gmail.com -port 587 -printCerts

        [S] 220 smtp.gmail.com ESMTP 6a1803df08f44-80166e2f32bsm34741116d6.41 - gsmtp
        [C] HELO localhost
        [C] EHLO localhost
        [S] 250-smtp.gmail.com at your service, [x.x.x.x]
        [S] 250-SIZE 35882577
        [S] 250-8BITMIME
        [S] 250-STARTTLS
        [S] 250-ENHANCEDSTATUSCODES
        [S] 250-PIPELINING
        [S] 250-CHUNKING
        [S] 250-SMTPUTF8
        [C] STARTTLS
        [S] 220-2.0.0 Ready to start TLS
        [C] EHLO localhost
        [S] 250-smtp.gmail.com at your service, [x.x.x.x]
        [S] 250-SIZE 35882577
        [S] 250-8BITMIME
        [S] 250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH
        [S] 250-ENHANCEDSTATUSCODES
        [S] 250-PIPELINING
        [S] 250-CHUNKING
        [S] 250-SMTPUTF8
        [C] QUIT
        [S] 221-2.0.0 closing connection 6a1803df08f44-80166e2f32bsm34741116d6.41 - gsmtp
        === TLS Connection Information ===
        TLS Version: TLS 1.3
        Cipher Suite: 0x1301
        Server Name: smtp.gmail.com
        Negotiated Protocol:
        Certificate Chain (3 certificates):
        --- Certificate 1 ---
        Subject: CN=smtp.gmail.com
        Issuer: CN=WR2,O=Google Trust Services,C=US
        Serial Number: 14461562026188826353951632455228095006
        Not Before: 2025-09-08T08:36:45Z
        Not After: 2025-12-01T08:36:44Z
        Is CA: false
        DNS Names: smtp.gmail.com
        Key Usage: Digital Signature
        Status: Valid
        --- Certificate 2 ---
        Subject: CN=WR2,O=Google Trust Services,C=US
        Issuer: CN=GTS Root R1,O=Google Trust Services LLC,C=US
        Serial Number: 170058220837755766831192027518741805976
        Not Before: 2023-12-13T09:00:00Z
        Not After: 2029-02-20T14:00:00Z
        Is CA: true
        Key Usage: Digital Signature, Certificate Sign, CRL Sign
        Status: Valid
        --- Certificate 3 ---
        Subject: CN=GTS Root R1,O=Google Trust Services LLC,C=US
        Issuer: CN=GlobalSign Root CA,OU=Root CA,O=GlobalSign nv-sa,C=BE
        Serial Number: 159159747900478145820483398898491642637
        Not Before: 2020-06-19T00:00:42Z
        Not After: 2028-01-28T00:00:42Z
        Is CA: true
        Key Usage: Digital Signature, Certificate Sign, CRL Sign
        Status: Valid
        --- Certificate Fingerprints (Leaf) ---
        SHA-1: 28:88:45:90:10:20:88:BA:87:2E:0E:7C:3A:12:D6:35:EC:26:AE:90
        SHA-256: 6F:F8:E2:F5:D4:AE:5A:FF:92:4A:5F:AC:88:80:14:3A:30:33:7A:CF:EE:33:94:82:EF:2A:93:47:80:E4:18:EF
        =====================================

           mailsend-go -info -smtp smtp.gmail.com -port 465 -ssl -printCerts

        [S] 220 smtp.gmail.com ESMTP 6a1803df08f44-80166781d27sm35134546d6.45 - gsmtp
        [C] HELO localhost
        [C] EHLO localhost
        [S] 250-smtp.gmail.com at your service, [x.x.x.x]
        [S] 250-SIZE 35882577
        [S] 250-8BITMIME
        [S] 250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH
        [S] 250-ENHANCEDSTATUSCODES
        [S] 250-PIPELINING
        [S] 250-CHUNKING
        [S] 250-SMTPUTF8
        [C] QUIT
        [S] 221-2.0.0 closing connection 6a1803df08f44-80166781d27sm35134546d6.45 - gsmtp
        === TLS Connection Information ===
        TLS Version: TLS 1.3
        Cipher Suite: 0x1301
        Server Name: smtp.gmail.com
        Negotiated Protocol:
        Certificate Chain (3 certificates):
        --- Certificate 1 ---
        Subject: CN=smtp.gmail.com
        Issuer: CN=WR2,O=Google Trust Services,C=US
        Serial Number: 14461562026188826353951632455228095006
        Not Before: 2025-09-08T08:36:45Z
        Not After: 2025-12-01T08:36:44Z
        Is CA: false
        DNS Names: smtp.gmail.com
        Key Usage: Digital Signature
        Status: Valid
        --- Certificate 2 ---
        Subject: CN=WR2,O=Google Trust Services,C=US
        Issuer: CN=GTS Root R1,O=Google Trust Services LLC,C=US
        Serial Number: 170058220837755766831192027518741805976
        Not Before: 2023-12-13T09:00:00Z
        Not After: 2029-02-20T14:00:00Z
        Is CA: true
        Key Usage: Digital Signature, Certificate Sign, CRL Sign
        Status: Valid
        --- Certificate 3 ---
        Subject: CN=GTS Root R1,O=Google Trust Services LLC,C=US
        Issuer: CN=GlobalSign Root CA,OU=Root CA,O=GlobalSign nv-sa,C=BE
        Serial Number: 159159747900478145820483398898491642637
        Not Before: 2020-06-19T00:00:42Z
        Not After: 2028-01-28T00:00:42Z
        Is CA: true
        Key Usage: Digital Signature, Certificate Sign, CRL Sign
        Status: Valid
        --- Certificate Fingerprints (Leaf) ---
        SHA-256: 6F:F8:E2:F5:D4:AE:5A:FF:92:4A:5F:AC:88:80:14:3A:30:33:7A:CF:EE:33:94:82:EF:2A:93:47:80:E4:18:EF
        SHA-1: 28:88:45:90:10:20:88:BA:87:2E:0E:7C:3A:12:D6:35:EC:26:AE:90
        =====================================

            mailsend-go -info -smtp smtp-mail.outlook.com -port 587 -printCerts

        [S] 220 MN2PR01CA0065.outlook.office365.com Microsoft ESMTP MAIL Service ready at Sat, 27 Sep 2025 00:29:10 +0000 [08DDFAA3FED0C1E0]
        [C] HELO localhost
        [C] EHLO localhost
        [S] 250-MN2PR01CA0065.outlook.office365.com Hello [x.x.x.x]
        [S] 250-SIZE 157286400
        [S] 250-PIPELINING
        [S] 250-DSN
        [S] 250-ENHANCEDSTATUSCODES
        [S] 250-STARTTLS
        [S] 250-8BITMIME
        [S] 250-BINARYMIME
        [S] 250-CHUNKING
        [S] 250-SMTPUTF8
        [C] STARTTLS
        [S] 220-2.0.0 SMTP server ready
        [C] EHLO localhost
        [S] 250-MN2PR01CA0065.outlook.office365.com Hello [x.x.x.x]
        [S] 250-SIZE 157286400
        [S] 250-PIPELINING
        [S] 250-DSN
        [S] 250-ENHANCEDSTATUSCODES
        [S] 250-AUTH LOGIN XOAUTH2
        [S] 250-8BITMIME
        [S] 250-BINARYMIME
        [S] 250-CHUNKING
        [S] 250-SMTPUTF8
        [C] QUIT
        [S] 221-2.0.0 Service closing transmission channel
        === TLS Connection Information ===
        TLS Version: TLS 1.3
        Cipher Suite: 0x1302
        Server Name: smtp-mail.outlook.com
        Negotiated Protocol:
        Certificate Chain (2 certificates):
        --- Certificate 1 ---
        Subject: CN=outlook.com,O=Microsoft Corporation,L=Redmond,ST=Washington,C=US
        Issuer: CN=DigiCert Cloud Services CA-1,O=DigiCert Inc,C=US
        Serial Number: 10535063011692331098818316272276424549
        Not Before: 2025-03-29T00:00:00Z
        Not After: 2026-03-28T23:59:59Z
        Is CA: false
        DNS Names: *.clo.footprintdns.com, *.hotmail.com, *.internal.outlook.com, *.live.com, *.nrb.footprintdns.com, *.office.com, *.office365.com, *.outlook.com, *.outlook.office365.com, attachment.outlook.live.net, attachment.outlook.office.net, attachment.outlook.officeppe.net, attachments.office.net, attachments-sdf.office.net, ccs.login.microsoftonline.com, ccs-sdf.login.microsoftonline.com, hotmail.com, mail.services.live.com, office365.com, outlook.com, outlook.office.com, substrate.office.com, substrate-sdf.office.com
        Key Usage: Digital Signature, Key Encipherment
        Status: Valid
        --- Certificate 2 ---
        Subject: CN=DigiCert Cloud Services CA-1,O=DigiCert Inc,C=US
        Issuer: CN=DigiCert Global Root CA,OU=www.digicert.com,O=DigiCert Inc,C=US
        Serial Number: 20058375873168194746987232153701302504
        Not Before: 2020-09-25T00:00:00Z
        Not After: 2030-09-24T23:59:59Z
        Is CA: true
        Key Usage: Digital Signature, Certificate Sign, CRL Sign
        Status: Valid
        --- Certificate Fingerprints (Leaf) ---
        SHA-1: A6:F7:EC:FB:2B:F6:31:B3:A8:4F:EB:B0:9F:FD:BB:4E:3B:0F:42:11
        SHA-256: 4F:94:1A:8E:50:52:5E:09:24:4F:8F:FE:75:65:E1:6A:51:DD:10:47:04:74:94:6A:0F:BA:84:6A:86:E4:DE:8C
        =====================================

  Use default settings for well known mail providers
Don’t worry about the settings of -smtp, -port and -ssl for well known mail providers. This works for gmail, yahoo, outlook, gmx, zoho and aol.

          mailsend-go -info -use gmail

  Send mail with a text message
Notice “auth” is a command and it takes -user and -pass arguments. “body” is also a command and here it took -msg as an argument. The command “body” can not repeat, if specified more than once, the last one will be used.

            mailsend-go -sub "Test"  -smtp smtp.gmail.com -port 587 \
             auth \
              -user jsnow@gmail.com -pass "secret" \
             -from "jsnow@gmail.com" -to  "mjane@example.com" \
             body \
               -msg "hello, world!\nThis is a message"

The embedded new line \n will be converted to a real newline and the final message will show up as two lines.

The environment variable “SMTP_USER_PASS” can be used instead of the flag -pass.

  Send mail with a HTML message

            mailsend-go -sub "Test"  \
            -smtp smtp.gmail.com -port 587 \
            auth \
             -user jsnow@gmail.com -pass "secret" \
            -from "jsnow@gmail.com"  \
            -to  "mjane@example.com" -from "jsnow@gmail.com" \
            body \
             -msg "<b>hello, world!</b>"

The environment variable “SMTP_OAUTH_TOKEN” can be used instead of the flag -token.

  Send mail with a HTML message, use XOAUTH2

            export SMTP_OAUTH_TOKEN='your_access_token'
            mailsend-go -sub "Test"  \
            -smtp smtp.gmail.com -port 587 \
            auth \
             -user jsnow@gmail.com \
             -oauth2 \
            -from "jsnow@gmail.com"  \
            -to  "mjane@example.com" -from "jsnow@gmail.com" \
            body \
             -msg "<b>hello, world!</b>"

  Attach a PDF file
MIME type will be detected. Content-Disposition will be set to “attachment”, Content-Transfer-Encoding will be “Base64”. Notice, “attach” is a command it took -file as an arg. The command “attach” can repeat.

            mailsend-go -sub "Test"  \
            -smtp smtp.gmail.com -port 587 \
            auth \
             -user jsnow@gmail.com -pass "secret" \
            -from "jsnow@gmail.com"  \
            -to  "mjane@example.com" -from "jsnow@gmail.com" \
            body \
             -msg "A PDF file is attached" \
            attach \
             -file "/path/file.pdf"

The name of the attachment will be file.pdf. To change the attachmetn name, use the -name flag. e.g.

            attach -file "/path/file.pdf" -name "report.pdf"

  Attach a PDF file and an image
Notice, the “attach” command is repeated here.

            mailsend-go -sub "Test"  \
            -smtp smtp.gmail.com -port 587 \
            auth \
             -user jsnow@gmail.com -pass "secret" \
            -from "jsnow@gmail.com"  \
            -to  "mjane@example.com" -from "jsnow@gmail.com" \
            body \
             -msg "A PDF file and a PNG file is attached" \
            attach \
             -file "/path/file.pdf" \
            attach \
             -file "/path/file.png"

  Attach a PDF file and embed an image
Content-Disposition for the image will be set to “inline”. It’s an hint to the mail reader to display the image on the page. Note: it is just a hint, it is up to the mail reader to respect it or ignore it.

            mailsend-go -sub "Test"  \
            -smtp smtp.gmail.com -port 587 \
            auth \
             -user jsnow@gmail.com -pass "secret" \
            -from "jsnow@gmail.com"  \
            -to  "mjane@example.com" -from "jsnow@gmail.com" \
            body \
             -msg "A PDF file is attached, image should be displayed inline" \
            attach \
             -file "/path/file.pdf" \
            attach \
             -file "/path/file.png" \
             -inline

  Set Carbon Copy and Blind Carbon copy

            mailsend-go -sub "Testing -cc and -bcc" \
            -smtp smtp.gmail.com -port 587 \
            auth \
             -user example@gmail.com -pass "secret" \
             -to jsoe@example.com \
             -f "example@gmail.com" \
             -cc "user1@example.com,user2@example.com" \
             -bcc "foo@example.com" \
             body -msg "Testing Carbon Copy and Blind Carbon copy"

Cc addresses will be visible to the recipients but Bcc address will not be.

  Send mail to a list of users
Create a file with list of users. The syntax is Name,email_address in a line. Name can be empty but comma must be specified. Example of a list file:

            # This is a comment.
            # The syntax is Name,email address in a line. Name can be empty but comma
            # must be specified
            John Snow,jsnow@example.com
            Mary Jane,mjane@example.com
            ,foobar@example.com

Specify the list file with -list flag.

            mailsend-go -sub "Test sending mail to a list of users" \
            -smtp smtp.gmail.com -port 587 \
            auth \
             -user example@gmail.com -pass "secret" \
                -f "me@example.com" \
                -to "xyz@example.com" \
                body \
                -msg "This is a test of sendmail mail to a list of users" \
                attach \
                    -file "cat.jpg" \
                 attach \
                    -file "flower.jpg" \
                    -inline \
                 -list "list.txt"

  Add Custom Headers
Use the command “header” to add custom headers. The command “header” can be repeated.

            mailsend-go -sub "Testing custom headers" \
            -smtp smtp.gmail.com -port 587 \
            auth \
             -user example@gmail.com -pass "secret" \
             -to jdoe@example.com \
             -f "example@gmail.com" \
             body -msg "Testing adding Custom headers"
             header \
                 -name "X-MyHeader-1" -value "Value of X-MyHeader-1" \
             header \
                 -name "X-MyHeader-2" -value "Value of X-MyHeader-2"

  Write logs to a file
Use the flag -log path_of_log_file.txt

            mailsend-go -sub "test log" \
             -smtp smtp.example.com -port 587 \
             auth \
              -user example@gmail.com -pass "secret" \
              -to jdoe@example.com \
              -f "example@gmail.com" \
              body -msg "Testing log file" \
              -log "/tmp/mailsend-go.log"

  Specify a different character set
The default character set is utf-8

            mailsend-go -sub "test character set" \
             -smtp smtp.example.com -port 587 \
             auth \
              -user example@gmail.com -pass "secret" \
              -to jdoe@example.com \
              -from "example@gmail.com" \
              -subject "Testing Big5 Charset" \
              -cs "Big5" \
              body -msg "中文測試"

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(Generated from docs/examples.md)

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Frequently Asked Questions (FAQ)
1. How to send mail via smtp.gmail.com?

From May 30, 2022, Google no longer supports the use of third-party apps to sign in to Google Account using username and password. However, an app-specific password can be set for mailsend-go to send mail via smtp.gmail.com. Here are the steps:

•   Login to your gmail account

•   Click on the Profile icon at the right side and then click on Manage your Google Account

•   Click on Security link from the list on the left sidebar.

•   Now you have to enable 2FA (Two Factor Authentication). Think carefully if you are going to do that for your main account. I used a test account and it does not seem to ask for 2FA code while sending email using smtp.gmail.com. However, it will require to enter 2FA code when you login to gmail.com. By default it sends 2FA code to your phone#, which is not secure. Configure to use Google Authenticator App instead for 2FA.

•   After 2FA is enabled, Click on Security link again. Select 2-Step Verification. Generate the app specific password by clicking on the App Passwords link. Specify mailsend-go as the app (I don’t think it matters).

•   Use the username and this app specific password to send mail via smtp.gmail.com. It does not seem to ask for 2FA code.

If there are any gotchas or need more clarification, please send a pull request or update Issue #49 with your experience and I will update the FAQ.

        -- updated: Jul-01-2022

License (is MIT)

        License is MIT
        Copyright © 2018-present muquit@muquit.com
        Permission is hereby granted, free of charge, to any person obtaining
        a copy of this software and associated documentation files (the "Software"),
        to deal in the Software without restriction, including without limitation
        the rights to use, copy, modify, merge, publish, distribute, sublicense,
        and/or sell copies of the Software, and to permit persons to whom the
        Software is furnished to do so, subject to the following conditions:
        The above copyright notice and this permission notice shall be included
        in all copies or substantial portions of the Software.
        THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
        EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
        OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
        IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
        DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
        TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
        OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

See Also
Original mailsend (https://github.com/muquit/mailsend) (in C)

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TOC is created by https://github.com/muquit/markdown-toc-go on Jun-21-2026