Re: [exim] Mail claims to be sent by my self

> From: Oliver von Bueren

> The error in the configuration
> is, that someone can send a message claiming to be from your local
> domain without authentication through your server.

On mailing lists for list moderators a common complaint is that
some list members never recieve their own messages back
(which might be possibly unapproved or edited by a moderator) -
the reason is that Gmail retains a copy of sent letter, and when
message comes back from a mailing list, Gmail sees the same Message-Id
and discards "a duplicate", members get annoyed.

Besides, the easiest and most convenient way to test for some mail problem
is to send a letter to one's own external forwarder which relays the letter
back to the owner of the forwarder. Forwarders on free mail services
usually don't alter envelope-from. Some listservers too.

Mail clients in some mobile phones have an option "copy to self"
(Bcc to the same address as in From). I use it. Some mobile operators
(mine included) closed port 25 and require to send through their relay.
Some mail clients in mobile phones may lack an option to send
to port other than 25 with authentication.

So, rejecting every message from your domain without authentication
is a bad idea. But in practice usual antispam means (in rcpt ACL)
fend off spam claiming to be from yourself as well as other kinds of spam.