msmtp - light SMTP client with support for server profiles

msmtp is an SMTP client that can be used to send mails from MUAs (mail user agents) like Mutt or Emacs. It forwards mails to an SMTP server (for example at a free mail provider), which takes care of the final delivery. Using profiles, it can be easily configured to use different SMTP servers with different configurations, which makes it ideal for mobile clients.

Installation

Install the msmtp package.

config example

You need to put your settings in ~/.msmtprc.

An example is provided in /usr/share/doc/msmtp/examples/msmtprc-user.example.

To send email via a Gmail account: 

# Set default values for all following accounts.
defaults
port 587
tls on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
logfile ~/.msmtp.log

account gmail
host smtp.gmail.com
from <user>@gmail.com
auth on
user <user>@gmail.com
passwordeval gpg --no-tty --quiet --decrypt ~/.msmtp-gmail.gpg

# Set a default account
account default : gmail

Others examples with debian.org and zoho + your domain: 

# Set default values for all following accounts.
defaults
tls on
auth on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
logfile ~/.msmtp.log

account zoho
port 465
host smtp.zoho.com
tls_starttls off
from <user>@your-domain.com
user <user>@your-domain.com
passwordeval gpg --no-tty --quiet --decrypt ~/.msmtp-zoho.gpg

account debian
host mail-submit.debian.org
port 587
tls_starttls on
from <user>@debian.org
user <user>
passwordeval gpg --no-tty --quiet --decrypt ~/.msmtp-debian.gpg

# Set a default account
# account default : debian
account default : zoho

Then store your credentials in a Secret Service compatible program such as keepassxc, gnome-keyring, kwalletmanager.

Otherwise, the credentials can be stored in an OpenPGP-encrypted password file, which can be created like this: 

$ gpg --encrypt --output=.msmtp-gmail.gpg --recipient=<user>@gmail.com - <<END
ThisIsMySeCrEtPassword
END

$ gpg --encrypt --output=.msmtp-zoho.gpg --recipient=<<user>@your-domain.com - <<END
ThisIsMySeCrEtPassword
END

$ gpg --encrypt --output=.msmtp-debian.gpg --recipient=<user>@debian.org - <<END
ThisIsMySeCrEtPassword
END

Make sure you don't forget the dash near the end, which causes gpg to use "standard input" to read the password of your private OpenPGP key. After you have launched this command, it waits for your password. Type your password, hit Enter and finish with Control-d. Then, gpg encrypts your password, stores the result into the file and terminates.

To test it, run: 

$ printf "To: _recipient_address_\n\nSubject: Test\n\nHello, This is my test message." | msmtp -a default _recipient_address_

gpg-agent will prompt you for your OpenPGP key passphrase when sending email.

Then you should find your sent e-mail in the _recipient_address_'s inbox shortly afterwards.

msmtp-mta

When a standard MTA interface is desired, but a full server like Postfix or Exim is not desired, then the msmtp-mta package can be a solution:

Install the msmtp-mta package.

The package provides a /usr/sbin/sendmail symlink to msmtp that other software can use to send mail. The msmtp-mta package also provides a msmtpd daemon that listens on 127.0.0.1:25. This is disabled by default. Keep in mind that the daemon has no way to know which user is connecting to it, so it has to way to use the user's .msmtprc. The system-wide /etc/msmtprc will still apply.

The MTA setup can be tested using with the mail program (provided by a package such as mailutils or bsd-mailx): 

$ mail -s "teste" address@email.com <<END
This is a test
END

If the above does not work, please report it through a bugreport. Try appending this line to /etc/mail.rc: 

set mta=/usr/bin/msmtp

Or try switching to a different package for the mail program.

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