Sendmail, 3rd Edition

Pitfalls

• The F=f and F=r delivery agent flags are similar in their implementation but can differ in their result. Consider, for example, the SunOS 4.x version of /bin/mail. That program expects the -r command-line argument to specify the sender’s name. Setting the F=r delivery agent flag correctly causes mail to be seen as being from the sender (-r sender), but mistakenly using the F=f delivery agent flag invokes /bin/mail with -f sender instead. This fails because the SunOS 4.x version of /bin/mail expects the -f command-line argument to mean that it should interactively read mail from the mailbox named sender.

• The F=C delivery agent flag can cause problems when it is specified for delivery agents for which the @domain form of address is inappropriate. This delivery agent flag should be avoided for DECnet and the local delivery agents. Note that LMTP-aware local delivery agents that can handle domain addresses can use this delivery agent flag.

• A common problem with SysV versions of /bin/mail is their annoying habit of prefixing a "From " line to the beginning of each message, even if one is already there. This confuses users because it makes their mail appear to come from uucp or daemon instead of the real sender. The problem stems from the fact that the SysV /bin/mail lacks a -r command-line argument (or its equivalent) to indicate who the sender is. Instead, that program assumes that the sender’s identity can be taken from the identity of the person who ran the program. This ...