The actual limit per folder is 1.000, but I have folders with nearly 10.000 mails. So aqua mail is the only known app usable.
For professional use as nearly the same like desktop application, the actual android app must be opened to 10.000 mails or better no unlimited.
There is a main page in aqua mail with all (in my case 2) mail accounts and the choosen 20 folders. Small letters, so no scrolling neccessary. I didn't look further for Thunderbird on Android due to the lack of loading a useful amount of messages per folder.