What is "No ! in UUCP! (user)" message from sendmail?

[Wietse Venema]

[Followups directed to comp.mail.sendmail]

tyager at maxx.UUCP (Tom Yager) writes:

>In attempting to send a mail message to any uucp destination, sendmail
>reports the error:
>   No ! in UUCP! (root)

This happens when sendmail tries to generate a UUCP-style mail header
line: "From <user> <date> remote from <host>" (see the 'U' flag in the
mailer program description).  Under this condition, sendmail wants an
address of the form:  <host!user>.  Your configuration file probably
produces the form:  <user at host>.  I ran into the same problem when I
needed both From_ lines and <user at host> in locally delivered mail, and
had to change two lines in some old sendmail source.