Android Sync Doesn't Work Too Good

Greetings,

I'm getting reports from a user who's reading and deleting mail on Thunderbird, but read flags and deletions don't show up in his Android phone. He's using the native Android mail app with the newest Android OS.

My question is, where do I start with troubleshooting this kind of issue? Thanks for anyone's insight here. We're using Dovecot 2.2.13.

-- --Asai