I have always suspected the problem lies within the email interface of awareim.
With regards to changing the password on the ISP side, I originally had the same issues, but then discovered if i changed the password on awareim side and then changed back to the original password it rectified the problem and email sending resumed.
So without changing the password at the ISP I was able to resolve the problem on my side.
I think somewhere in the process of sending, Awareim email interface gets corrupted from time to time(under certain conditions) resulting in the block.
I must say its been quite sometime since I have had the problem, but i f it does happen I use the same procedure to resolve the issue. It might be a good idea to periodically run a background process that changes the email password back and forth to remedy the problem