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msmtp is a basic email sender client. It is easy to configure but lacks some features like queuing when offline.


A minimal configuration to relay mails through an external mail server coud look like this

Warning: Do not use a plaintext password in production, this is for demonstration only
programs.msmtp = {
  enable = true;
  accounts.default = {
    host = "";
    from = "";
    user = "";
    password = "mypassword123";

In this case msmtp will try to deliver mails through the smtp server on port 25. user and password are used for normal plaintext authentication.

This configuration will automatically set msmtp as the default mail delivery client on your system by overwriting the sendmail binary. To test mail delivery issue following command:

# echo -e "Content-Type: text/plain\r\nSubject: Test\r\n\r\nHello World" | sendmail

A mail with the subject Test" will be send to the recipient including the body text Hello World. A Mime-Header is added to the mail content for better compatibility.


Further configuration options for msmtp can be found here.

TLS connections

programs.msmtp = {
  enable = true;
  accounts = {
    default = {
      auth = true;
      tls = true;
      # try setting `tls_starttls` to `false` if sendmail hangs
      from = "<from address here>";
      host = "<hostname here>";
      user = "<username here>";
      passwordeval = "cat /secrets/smtp_password.txt";

Note that msmtp has no daemon and runs as the invoking user. If using passwordeval, the file must be readable by any user that wishes to send mail.



programs.msmtp.defaults = {
  aliases = "/etc/aliases";

environment.etc = {
  "aliases" = {
    text = ''
    mode = "0644";

See also