well I was about to migrate to AWS from smartermail (which completely ruined my trust with their handling of their disastrous zero day) when I read this. I am in the market for a replacement too.
Looking for a provider handling custom domains, aliases, enabling to send emails from an alias and with an API to create/delete aliases programmatically, with a decent webmail + ActiveSync or equivalent for easy smartphone config + push.
So far it seems to me that the only options are Exchange 365 and Google. But I fear those will be over engineered and super complicated to set up.