Using Aquamail on Android device; suddently could not send from that device. Aquamail reports "authentication error 500 5.7.0 Unknown AUTH error -1 (Internal authentication error)"
Thanks to diligence by Kostya Vasilyev at Aquamail, problem solved: http://www.aqua-mail.com/?p=1716. No thanks to Verizon. Their page on email settings is frustratingly incomplete when the mail client has deep capability on authenticatiopn and encryption.
A little more forethought, Verizon, and maybe consideration of the trouble you can inflict on customers.