Sendmail, 3rd Edition

Pitfalls

• Sending a great deal of email really fast is a very complex configuration problem. In addition to the topics covered in this chapter, learn everything you can about building the sendmail binary (Chapter 3), all the sendmail options (Chapter 24), and all the available mc configuration features (Section 4.8 in Chapter 4). It is only through a full understanding and judicious use of these that you can maximize delivery speed.

• Never use the techniques in this chapter to send unsolicited (spam) email even accidently. When testing a new setup, it is very easy to forget that you are connected to the real Internet. Avoid, for example, the temptation to maintain two configuration files, one with the ConnectOnlyTo option defined to send test email to a blackhole machine, and another with that option undefined, to send real email to the Internet. With such a setup, it is easy to accidentally send test email to the Internet using the wrong configuration file.

• When using V8.12 and above sendmail, avoid moving queue files around yourself. The qf file, for example, internally stores the full pathname of the df file’s directory, so you need to edit that line as part of a move. Also, sendmail can split messages at message submission time into multiple qf files, possibly in different queues, all sharing a df file with hard or symbolic links to it. This complexity makes queue file moves a complex undertaking.