Thanks so much for the reply!
I did what you said and it has worked, the only problem I am getting now is the following.
I can see the mail being tranferred to my mail server, my mail server then tries to send the mail onto my cliets mailbox hosted on another server and it gets connection timed out.
Not sure why because if I send him a mail from my gmail account it works.
See below error from log.
postfix/smtp: 6B2D2C81C5: to=<info@XXXXX.co.za>, relay=none, delay=21, delays=0.07/0.01/21/0, dsn=4.4.1, status=deferred (connect to mail.XXXXX.co.za[96.213.XXX.XX]:25: Connection timed out)
I've crossed out some info for security reasons, hope this doesn't affect anything for for.