Unable to send email with sendmail from PHP 5.3 on CentOS VM

Linux and Unix-Like Linux
1

I have a longstanding issue on my CentOS 5.6 VM where I am unable to send email from my PHP application.

This is the last bunch of lines from my /var/log/maillog file.

Feb 14 10:29:16 dev53 sendmail[4637]: s1EATEEo004637: Authentication-Warning: www.craig.dev-crmpicco.lan: apache set sender to client.care@crmpicco.co.uk using -f
Feb 14 10:29:16 dev53 sendmail[4637]: s1EATEEo004637: from=client.care@crmpicco.co.uk, size=11017, class=0, nrcpts=0, msgid=<1392373753.d4a897919a124958e699170b2b1dc8f2@PHPMAILSERVER>, relay=apache@localhost
Feb 14 10:29:16 dev53 sendmail[5119]: s1EATG5R005119: Authentication-Warning: www.craig.dev-crmpicco.lan: apache set sender to client.care@crmpicco.co.uk using -f
Feb 14 10:29:16 dev53 sendmail[5119]: s1EATG5R005119: from=client.care@crmpicco.co.uk, size=9507, class=0, nrcpts=1, msgid=<1392373756.8e5e15c4e6d09c8333a17843461041a9@PHPMAILSERVER>, relay=apache@localhost
Feb 14 10:29:16 dev53 sendmail[5135]: s1EATGpY005135: from=<client.care@crmpicco.co.uk>, size=9684, class=0, nrcpts=1, msgid=<1392373756.8e5e15c4e6d09c8333a17843461041a9@PHPMAILSERVER>, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1]
Feb 14 10:29:16 dev53 sendmail[5119]: s1EATG5R005119: to=cmorton@crmpicco.co.uk, ctladdr=client.care@crmpicco.co.uk (48/48), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=39507, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (s1EATGpY005135 Message accepted for delivery)
Feb 14 10:29:18 dev53 sendmail[5199]: s1EATGpY005135: to=<cmorton@crmpicco.co.uk>, delay=00:00:02, xdelay=00:00:02, mailer=esmtp, pri=129684, relay=smx1.crmpiccov3.co.uk. [217.158.143.122], dsn=5.7.1, stat=User unknown
Feb 14 10:29:18 dev53 sendmail[5199]: s1EATGpY005135: s1EATIpY005199: DSN: User unknown
Feb 14 10:29:18 dev53 sendmail[5199]: s1EATIpY005199: to=<client.care@crmpicco.co.uk>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=40917, relay=smx1.crmpiccov3.co.uk. [217.158.143.122], dsn=5.7.1, stat=User unknown
Feb 14 10:29:18 dev53 sendmail[5199]: s1EATIpY005199: s1EATIpZ005199: return to sender: User unknown
Feb 14 10:29:18 dev53 sendmail[5199]: s1EATIpZ005199: to=root, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=41941, dsn=2.0.0, stat=Sent

I know for certain that the issue is not with the PHP code as the exact same code works in the office, however when WFH (on a seperate VM with the same code) I am unable to send emails.

I am trying to establish if this is because of my sendmail setup, IP whitelisting at the mail server end or hosts file setup or anything like that?

Note: I have masked the true name of the domain for security reasons for this post.

2

The destination user cmorton seems to be unknown for crmpicco.co.uk

...to=<cmorton@crmpicco.co.uk>...User unknown...
3

It turns out this is due to Spam Filtering at the mail server end:

When I look at the messages sitting in my mail log that have been returned I get a link to this:

IP Address Classification Lookup | Sophos Threat Center | SophosLabs

So it would appear to be a configuration issue with the mail server.