How Can I Send Emails Without Using an SMTP Server?

How to Send Emails without an SMTP Server

While most email transmission requires an SMTP server, there is an alternative method to avoid third-party server limitations.

Delegating to External Programs

The only way to send emails without direct SMTP communication is to entrust the task to another program. This program can be a range of options, but POSIX systems often utilize the binary /usr/sbin/sendmail or /usr/bin/sendmail.

Calling Sendmail with /usr/sbin/sendmail

Calling this program with the -t command-line option allows it to read recipient addresses from the email headers. You can use os/exec, net/mail, and net/textproto to manipulate the piping and text.

Using the gomail Library

Alternatively, the gomail library provides a simplified interface for sending emails through Sendmail. Its Message type offers the WriteTo() method, which connects a mail message to the running Sendmail instance.

Advantages of Using an MTA

Although delegating to an external program is viable, using a full-blown Mail Transfer Agent (MTA) like Sendmail offers the benefit of mail queuing. An MTA can temporarily hold emails if immediate delivery is not possible and continually attempt to send it until it succeeds or a significant timeout lapses.

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