Automated Mail Purging for SMTP Mail

Mr. Keller gives us three scripts for cleaning out old mail files automatically.
Installation

Copy the scripts to your favorite directory. I used /usr/local/bin. Edit mailrm.sh and mailage.sh to reflect your mail directory and the location of formail. Then just run the script with the number of days to retain messages as its argument. For example, to purge messages older than 60 days:

/usr/local/bin/mailrm.sh 60
What Could Be Done Better

Is this mail purge solution perfect? No, it does nothing to lock mail files, which could pose a problem if a user's mail client polls frequently or this job runs during busy hours. Some possible steps to address this could include stopping sendmail while the scripts run, preventing the POP3 server from running and tightening permissions on the mail directory to prevent access from non-superusers. Since it would normally run in the early-morning hours via cron, the probability of collision would be low.

Also, this solution relies on external utilities that may not function as expected. formail might not properly handle all the mail headers, though I haven't encountered problems yet. cat might not like some characters that could appear in messages, resulting in lost message text. I've had few problems with cat, but your experience may be different.

The date conversion logic in maildate.sh is simplistic. It's not accurate for the year 1900, and the leap year calculation will not work correctly after the year 2099. However, it works well for calculating the difference between two dates, and it's reasonably fast.

Since I use three scripts to get around parameter-passing limitations in Bash, this package runs more slowly than it might (because of having to fork processes repeatedly). Recoding the scripts into a single Perl script might help—my Perl skills are too limited for this project.

Conclusion

If you have a need for automated mail purging, these scripts can help you reach your goal. At least, they may give you ideas for your own solution. If you create a more elegant solution, I'd like to hear about it.

Resources

All listings referred to in this article are available by anonymous download in the file ftp://ftp.linuxjournal.com/lj/listings/issue47/2118.tgz.

Michael S. Keller (mskeller@paranet.com) is a Technical Analyst with Paranet, Inc., a nation-wide network services provider owned by Sprint. He has used computers for twenty years and Unix variants for seven. Paranet's virtual home is at http://www.paranet.com/.

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