I am experiencing an issue where my CentOS 5.6 (Final) VM running on Windows 7 has stopped sending emails from my PHP code.

I'm confident this isn't a coding issue as I have the exact same code running in my office and emails send correctly from there, hence why I believe this to be a networking/configuration issue.

In my /etc/hosts/ file on my VM I have the following:

Code:
127.0.0.1 localhost.localdomain localhost
192.168.0.9 crmpicco.co.uk m.crmpicco.co.uk dev53.localdomain
When I run setup on my VM the DNS configuration is set to dev53.localdomain and my Primary DNS is 192.168.0.1.

In My /var/log/maillog files I see a lot of this sort of thing:

Code:
Nov 19 14:36:58 dev53 sendmail[21696]: qAJEawI7021696: from=<client.care@crmpicco.co.uk>, size=12858, class=0, nrcpts=1, msgid=<1353335817.9103820024efb30b451d006dc4ab3370@PHPMAILSERVER>, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1]
Nov 19 14:36:58 dev53 sendmail[21693]: qAJEawvd021693: to=newbie@fletcher.co.uk, ctladdr=client.care@crmpicco.co.uk (48/48), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=42681, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (qAJEawI7021696 Message accepted for delivery)
Nov 19 14:36:59 dev53 sendmail[21698]: qAJEawI7021696: to=<newbie@fletcher.co.uk>, delay=00:00:01, xdelay=00:00:01, mailer=esmtp, pri=132858, relay=mailserver.fletcher.co.uk. [213.171.216.114], dsn=5.0.0, stat=Service unavailable
Is this likely to be a configuration issue?