Mailers

A mailer is a sendmail specific term. You can customize amail delivery agent. A mailer is used by sendmail to identify a specific instance of a customized mail delivery agent or a mail transport agent.

You need to specify at least one mailer in the sendmail.cf file of all systems in your network.

The ether mailer uses the SMTP protocol to transport a message. SMTP is the standard mail protocol used on the Internet. This is an example of an SMTP mail header:

To: paul@phoenix.stateu.edu
From: Iggy.Ignatz@eng.acme.com

If mail is sent between two users in the same domain, the header looks like this:

To: Irving.Who@eng.acme.com
From: Iggy.Ignatz@eng.acme.com

Use SMTP for sending mail outside your domain, especially for mailboxes that you must reach through the Internet.

The smartuucp mailer uses uux to deliver messages, but it formats headers with a domain-style address, and the To: and Cc: lines are formatted by domain, much like the SMTP headers. The smartuucp headers look like this:

To: paul@phoenix.stateu.com
From: ignatz@eng.acme.com

Use smartuucp for UUCP mail to systems that can handle and resolve domain-style names. The sender also must be able to handle domain-style names and be able to receive replies from the Internet.

The uucp mailer uses an exclamation point address in the headers. This is one of the original mailers. The headers look like this:

To: edu!stateu!phoenix!paul
From: acme!ignatz

You can define other mail delivery agents by providing a mailer specification in the sendmail.cf file.