The sendmail program, by means of aliases or ~/.forward files, is able to deliver mail directly to files on disk (Section 12.2.2). The form for delivery to files looks like this:
Here, mail addressed to the user-id ident at your site will have each message appended to the file indicated by the path /path/to/file. This technique is often used to archive mail messages to mailing lists. A typical application might look like this:
volleyball: karch, flo, wilt, karolyn, /etc/mail/archives/volleyball.archive
Here, mail sent to the mailing list volleyball, will be delivered to the four individuals shown. The message will also be appended to the file volleyball.archive.
The ability to append to files is one of the sendmail program’s strengths. Delivery to files in the aliases file is a convenience for the system administrator and mailing lists managers, but it was never designed or intended to be a robust mechanism for handling high volumes of message delivery to files.
Ordinarily, the sendmail program’s ability to write to files works just fine. But at some sites the file-locking part of that writing can lead to contention problems. To illustrate, consider the following scenario, one that is more common than you would expect.
When handling many busy mailing lists, you will soon discover that, over a surprisingly short period of time, about 10% of the addresses in those lists will become bad. A user can move from one ISP to another, ...