I get this error sporadically and not at all some days and continually other days. First, authentication fails… I will get the failure message. and most of the time if I click OK it will authenticate. However here is a very annoying problem with EM Client. If I am busily typing away in some document and authentication failure occurs, the failure message switches my cursor focus to the password field and if I don’t notice, I will over type my password. Then of course my password is wrong because I just retyped it. Please stop EM Client from doing that.
Then occasionally even if I click OK to cause it to re-try authentication, it will simply fail and then I get the second error message about the base 64 error.
When I run diagnostics on the POP3 and SMTP, it says all is OK.