70 Mail
I had fun with my own mailer-error-of-the-day recently. Seems I got
mail from someone in the “.at” domain. So what did the Unix mailer
do with this address when I tried to reply? Why it turned “at” into
“@” and then complained about no such host! Or was it invalid
address format? I forget, there are so many different ways to lose....Or perhaps sendmail just thinks that Judy shouldn’t be sending e-mail to
Austria.STEP 3: Figure out where it goes.
Just as the U.S. Postal Service is willing to deliver John Doe’s mail
whether it’s addressed to “John Doe,” “John Q. Doe,” or “J. Doe,” elec-
tronic mail systems handle multiple aliases for the same person. Advanced
electronic mail systems, such as Carnegie Mellon University’s Andrew
System, do this automatically. But sendmail isn’t that smart: it needs to be
specifically told that John Doe, John Q. Doe, and J. Doe are actually all the
same person. This is done with an alias file, which specifies the mapping
from the name in the address to the computer user.Alias files are rather powerful: they can specify that mail sent to a single
address be delivered to many different users. Mailing lists are created this
way. For example, the name “QUICHE-EATERS” might be mapped to
“Anton, Kim, and Bruce.” Sending mail to QUICHE-EATERS then results
in mail being dropped into three mailboxes. Aliases files are a natural idea
and have been around since the first electronic message was sent.Unfortunately, sendmail is a little unclear on the concept, and its alias file
format is a study in misdesign. We’d like to say something insulting, like
“it’s from the dark ages of computing,” but we can’t: alias files worked in
the dark ages of computing. It is sendmail’s modern, up-to-date alias files
that are riddled with problems. Figure 1 shows an excerpt from the send-
mail aliases file of someone who maintained systems then and is forced to
use sendmail now.Sendmail not only has a hopeless file format for its alias database: many
versions commonly in use refuse to deliver mail or perform name resolu-
tion, while it is in the processing of compiling its alias file into binary for-
mat.