OT: Sendmail weirdness

[Chris Yuzik]

Sorry for posting a sendmail question here. I've asked on a forum and on 
  usenet but haven't gotten a usable response yet, and the people on 
this list tend to have "guru status" at almost everything server related.

I recently discovered that our system (Centos 4.4, Sendmail, Procmail, 
etc.) is ignoring users' .forward files even though they seem to be 
correctly formatted. At first I thought it might be a permissions issue, 
as I remember reading that if the permissions on the .forward file, or 
the dir or any parent subdirs its contained in must not be world 
writeable. The permissions are fine in all cases.

Further investigation points to the format of the user accounts, in that 
everyone's user account is in the format of "user at domain.tld" and 
apparently sendmail doesn't process a .forward file if there is an "@" 
in the account name.

The following seems to indicate that the .forward file is not even 
looked at.

#sendmail -d27.2 -bv testuser at testdomain.com
testuser at testdomain.com... deliverable: mailer local, user 
testuser\@testdomain.com

One person indicated that there is likely a directive or something to 
put in the sendmail.cf file to change this behaviour, but I have been 
unable to find anything. Searching for help on this is particularly 
tricky as Google seems to ignore the "@" or the "\" sign from searches.

Can anyone help?