Message acquisition seems to be based on a random set of rules, rather than when a message has been received at the inbox. Sent an email with attachment I wanted to my phone, only for it not to arrive. I've done this before and it's usually only taken an hour or so, but this simply wasn't coming, so opened a hotmail account out of frustration.
Email arrived within moments.
I have no idea whose fault this is, nor do I care, but it's a pain in the proverbial. At least I can get emails to the phone reliably now.