FAQ / Policy controls / Q0732
Q0732
Question
I would like to either warn or deny when a host uses an underscore in the EHLO command.
Answer
First, set
helo_allow_chars = _
This tells Exim not to reject the EHLO or HELO command immediately. Once you have done that, you can test for the underscore in an ACL. For example, to log a warning for hosts in your LAN, and reject for other hosts, you could do something like this:
deny message = Underscores are not valid in host names
hosts = ! +lan_hosts
condition = ${if match{$sender_helo_name}{_}{yes}{no}}warn log_message = Accepted underscore from [$sender_host_address]
condition = ${if match{$sender_helo_name}{_}{yes}{no}}
FAQ / Policy controls / Q0732