1) Sending to a gmail account from SM server email account - works
2) Sending to an email on my SM server from a hotmail account - works
3) Sending to an email on my SM server from an outlook account - works
4) Sending to an email account on a fasthosts server from a gmail account - works
5) Sending to any email on my SM server from a gmail account - never arrives, nothing in the logs, no bounces, no errors in gmail!
6) Blacklist check - clear
So it's only the gmail emails that aren't arriving, and I have no way of telling why as there are no errors or anything in the logs.
Any idea how I can resolve?