I also had the same issue when gpg was used and it didn't work when I switched to plain text either until I deleted the .config/cgmail/accounts.ini file (which was still being setup as if it was using gpg - ie no uid/passwords).
I also had the same issue when gpg was used and it didn't work when I switched to plain text either until I deleted the .config/ cgmail/ accounts. ini file (which was still being setup as if it was using gpg - ie no uid/passwords).