Is there a guide to configuring email support with XG 17.5.7?

I never though enabling email support would be so much trouble. Is there a guide to configuring email support - basically SMTP & IMAP - through the XG firewall (home edition) that actually works? I think I have followed every article on the community with no success.

I have a pretty simple home network - ADSL2 connection, XG home firewall, a synology NAS with mailplus server. I want to be able to send and receive email from my home devices (iPhone, iPad) from a mailbox on my NAS. I have been able to get outgoing SMTP working, but incoming  SMTP fails miserably. I can’t even turn off the autocreated rules and send port 25/587 traffic directly in/out with no processing. I have tried a direct DNAT type rule for incoming SMTP but it still won’t pass the traffic through. A telnet on port 25 to my firewall from the internet goes unanswered and times out. The email templates for business application rules don’t have a field to say where the email traffic should go (i.e. to the mail server on the NAS), even though the action says ‘forward’.

I thought I knew the basics of firewall configuration reasonably well, but this has beaten me.

Any basic guides would be appreciated before I give up and try a different product.

Thanks.