I sent a posting to this list.
The list did a Call-out
-----------------------------------
exim-users@???
SMTP error from remote mail server after end of data:
host tahini.csx.cam.ac.uk [131.111.8.192]: 550-Verification failed for <exim@???>
550-Called: 95.172.15.115
550-Sent: RCPT TO:<exim@???>
550-Response: 550 [2C08] Rejected. Sender's email address invalid:
550 Sender verify failed
--------------------------------------
and I got:-
-------------------------------------
REJECTED
Server's IP : 131.111.8.192 => tahini.csx.cam.ac.uk => 131.111.8.192
Server's HELO : tahini.csx.cam.ac.uk => 131.111.8.192
Server's port : 45511
Our server : m2.u226.com
Date : Saturday, 01:01:02, 23 August 2014 (+01:00)
Sender :
Recipient : exim@???
Message-ID :
Report : [2C08] Invalid sender email address
------------------------------------------
The query I would like to submit is, should Exim Call-outs include a VALID email address, or at least use a Internet domain name having a MX entry ?
Exim Call-outs force us to accept emails with no sender's email address. Is this policy wise as it provides another opportunity for spammers and virus distributors to penetrate the first layer of our defences ?
A significantly large quality of spam can be successfully rejected by refusing mail having
ACL Connection
1. no host name
2. no reverse DNS
3. host name being generically similar to home Internet connection (e.g. 1.2.3.4-dynamic.spam.int)
ACL HELO
4. no HELO/EHLO or HELO/EHLO having the host's IP address
5. HELO/EHLO name has no IP address
6. HELO/EHLO name's IP address not resolving to host's IP address
7. HELO/EHLO being our's.
and that is merely a beginning with more in ACL RCPT including checking for a MX entry.
Paul.
