This has been a problem since the very beginning, and I'd really like to know whether it'll ever be fixed. Or at least have an explanation as to how it works so we know what to expect in game when wanting to receive mail.

Sometimes I'll get really lucky, and an item I purchase or have sent to me will come through right away. I'm always amazed when this happens.
Other times, I can zone or travel to a wayshrine (anything with a loading screen) and mail will then come through. Kind of a pain, but not the worst when it works.
And pretty often, mail will not come through until I actually log out to character select, and log back in. I've basically resorted to doing this almost every time I want mail to work, as it's the only thing that works every time.

There has to be something triggering a push for in game mail when we zone or log in. Why can't this same trigger just occur naturally when an item is sent or purchased? It's been two years since launch and it's just starting to feel like such a clumsy oversight that we don't have a reliable in game mail system.

Is the system inherently flawed to the point that it'll just never work the way we'd expect? Or are improvements possible but difficult to implement?