Sendmail works through sending to a smarthost, but can't find local users.

# sendmail -bv  [email protected]
[email protected]... User unknown
# grep LocalUser /var/log/maillog
Sep  8 03:48:30 myhost sendmail[6678]: r887mUs3006678: [email protected]... User unknown

but ...

# ls /home|grep LocalUser

and ...

# grep LocalUser /etc/passwd

How can I configure sendmail to find localusers? How should I diagnose this?

1 Answer 1


Sendmail and local users with uppercase letters


Sendmail's default configuration converts local user/mailbox names to all lowercase letters before delivery attempt. In your case email to [email protected] is delivered by sendmail to non existing localuser instead of existing LocalUser.

Possible fixes

Do not use usernames with uppercase letters


Specify the only right uppercase and lowercase mix (fox given lowercase only string). It requires modification in sendmail.mc and aliases files.

Subject: Q4.17 -- How do I handle user names with upper-case characters?

sendmail.mc file (requires recompilation into sendmail.cf file):


aliases file (requires recompilation with newaliases command):

# lowercase version to real for accounts with uppercase letters
localuser: LocalUser

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