Is this a POP3 or an IMAP account?
Could you record a debug log as described below?
http://www.aqua-mail.com/?page_id=232---
In the application’s settings, open “Debug” section (at the bottom) and enable “Debug logging” there. Set “Log output location” to “Root of memory card”. You will need to enable “Include raw data” most of the time, if the issue is related to specific message(s) or account(s).
Once logging is enabled, please repeat whatever was causing the issue.
After having done this, you can disable logging and send the log file, stored at the root of your device’s memory card
and called log-AquaMail.txt, to kmansoft / at sign / gmail / dot com.
The log does not contain your email account passwords.
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While the log in enabled, please be sure to capture the issue: empty the trash, and then run a sync.