(NOTE:  This is probably obsolete, but we are leaving it in for the time being.)

I keep getting error mail that has a bad return path, e.g., "Return-Path: <<@@somehost.com>>". Why is LISTSERV doing this?

The answer is that LISTSERV isn't doing this. You have a bug in sendmail, probably as a result of a bad rewrite rule in sendmail.cf. The Return-Path: line is inserted by sendmail as it delivers the message, not by LISTSERV. (This can also apply to Windows servers that are using a sendmail machine as their SMTP_FORWARD host.)

If you are running a sendmail version prior to version 8.7.x, the simple solution to this problem would be to upgrade your sendmail to the latest UCB version (we do not recommend using OEM versions because our experience with them indicates that the OEM usually introduces some kind of error in sendmail.cf that doesn't play well with LISTSERV). Version 8.7.x (and later; 8.15.2 is the latest available version at this writing) has a much-simplified sendmail.cf that eliminates most of the chance for error on a standard installation.

If you are running a sendmail earlier than 8.7.x, please note that the official sendmail distribution site (ftp://ftp.cs.berkeley.edu/ucb/sendmail/.message) currently notifies users that "8.6 is not supported, not secure, and should not be run on any network-connected machine."