Re: [Exim] Re: misconfigured mail server

Patrick Starrenburg wrote:

> Better thing to do would be to have some way of catching them and send a
> notice to sending user and postmaster every time that their systems and/or
> administrators :-) are misconfigured. Or have option to reject with a 5xx
> error so the sender knows problem straight away.
>

As of Exim 4.20 you can do this yourself. Leave '_' in helo_allow_chars,
but then put a rule into an ACL used at acl_smtp_helo to check for the
underscore. If it's there, do a "deny", which causes Exim to send a 5xx
code I believe.