I can’t figure it out, these email things are tricky in SuiteCRM unless you go full debug mode with an IDE and Xdebug, stepping through the code…
This issue seems different from yours, but you have some log messages in common. Have a look to see if any of that discussion seems helpful to you:
You seem to be hitting some difficulty or bug opening up the IMAP folder, and from then on it’s just a sequence of FATALs due to that original problem. But I don’t know why that happens in the first place 
@pstevens if you have any ideas, please chime in