I have set GMS Mail to force APOP authentication for all clients but I cannot get this to work with Outlook Express. Why is this?
Outlook Express does not support the use of the standard APOP Protocol as defined by RFC 1939.
Outlook Express instead uses Secure Password Authentication (SPA) which is not the same as APOP. Secure Password Authentication relies on an additional extension to the above RFC called AUTH.
Servers that support this return AUTH as one of the supported capabilities to the CAPA command. Gordano’s POP server supports the AUTH command in builds later than 3037.
Keywords:APOP outlook express auth pop