I have just installed Debian Squeeze x64 and tried sending myself a test email from it using the normal "mail" command. When I sent it I got this error from Exim:
2013-06-08 08:12:46 Exim configuration error in line 173 of /var/lib/exim4/config.autogenerated:
user uucp was not found
Can't send mail: sendmail process failed with error code 1
After a bit of research into this it sounds like all Debian systems should have the "uucp" user, but can I just run "useradd uucp" or does it need setting up to own certain directories and stuff?