Testing smtp auth can be a bit of a pain sometimes, particularly if SSL or TLS is involved. Mail clients often don’t really show what they are doing and/or don’t allow you to set all variables, like which authentication mechanism to use.
John M. Simpson has a nice page that describes how to do AUTH PLAIN by hand, but it does not cover AUTH LOGIN or CRAM-MD5.
Enter this really nice tool: mailsend. It compiles cleanly, is fast, and allows you to test AUTH PLAIN, AUTH LOGIN and AUTH CRAM-MD5 quickly and easily. Thank you, Muhammad A Muquit!