Update,

My apologies for not updating this post sooner but have been extremely busy at work.

It turns out that there was nothing wrong with my Turnkey Linux install after all.

Email was being sent out but not reaching clients because the Amazon E2C elastic IP is listed in Spamhaus.

I am trying additional elastic IPs and checking to see if they are listed in Spamhaus.

Does anyone have another solution?

Regards

David