For a sender callout check, Exim makes SMTP connections to the remote
hosts, to test whether a bounce message could be delivered to the sender
address. The following SMTP commands are sent:
HELO </primary host name/>
MAIL FROM:<>
RCPT TO:</the address to be tested/>
QUIT
. . .
From some mail server we obtain:
2005-02-08 11:12:55 H=(host.remote_domain.local) [213.183.154.54]:30396
I=[212.210.229.6]:25 sender verify fail for <aaaa@remote_domain.com>:
response to "MAIL FROM:<>" from mail.remote_domain.com [83.103.57.67] was: 550 Sorry, this server is configured to refuse this sort of mail
to combat the SPAM problem)