The fax delivery agent is used to deliver mail to a fax-sending program. If you define this delivery agent with:

MAILER(`fax')

any address that ends in .fax is automatically sent to that delivery agent. Thus, to fax mail to a user on the local machine, you might do the following:

To: joe@5554321.fax

This will cause the message to be sent to the faxmail program for delivery to the number 555-4321.^[5] The faxmail program will parse the message for a recipient, and for fax-tuning parameters passed in header lines that begin with x-fax-. It will format and send the result to the hfaxd daemon, which actually communicates with fax modems.

^[5] Note that in the United States, numbers that begin with 555 (other than 555-1212) are guaranteed to be non-existent or benign. That is why 555 numbers are often used in U.S.-produced movies and television programs (and in examples in books such as this).

Note that hfaxd and the modems need not exist on the local machine. If you have a central fax server, you can set up all the client machines by defining the FAX_RELAY mc configuration macro to point at that machine:

define(`FAX_RELAY', `fax.your.domain')

With this definition, any mail addressed to an address ending in .fax will be forwarded to fax.your.domain for sending as a fax. Obviously, you will need to have fax-sending software and fax modems installed on that machine.

Note that you should use either MAILER('fax') or FAX_RELAY—not both. If you declare both, the MAILER('fax') will supersede the FAX_RELAY, and all fax mail will be delivered locally.

Another way to handle faxes is to set up aliases for each user that can receive faxes:

userA+fax: "|/usr/local/bin/faxmail -d userA@5551234"
userB+fax: "|/usr/local/bin/faxmail -d userB@5556789"

The defaults for the fax delivery agent are listed in Table 20-6. The mc configuration macros at the left can be used to modify or replace those defaults.

The faxmail program, the hfaxd daemon, and all the other supporting software you need to email faxes is available from ftp://ftp.hylafax.org/.

Also, a number of commercial products are available that allow users to email faxes. They are easily found by searching on the Web.