inet messages with attachments can't be fetched w/IMAP ssl

Problem discovered using NotifyLink, but repeatable using Outlook Express - email coming from internet with attachments cannot be fetched using IMAP over SSL. Switched to regular IMAP, and problem goes away. NotifyLink gives error 371, Outlook Express says:

Outlook Express could not download the requested message. It is likely that the message was removed or expired from the server. A message could not be downloaded from the IMAP server. Subject 'test message', Account: 'servername', Server: 'servername', Protocol: IMAP, Server Response: 'UID FETCH (8209)', Port: 993, Secure(SSL): Yes, Error Number: 0x800CCCD2

Running IMAP on GWIA on W2008, recently upgraded to GW 2012. (Could the self-signed cert created with the GWCSRGEN utility be at play here?)

Alternatively, tried to switch to non-SSL by changing SSL from "Required" to "Enabled", but server still responding "NO LOGIN Connection must be encrypted" despite toggling settings and restarting GWIA. The docs say "If SSL is "Enabled", and the client can perform SSL, SSL will be used." But it would seem that "Not required/Enabled" would allow non-SSL connections if requested over port 143, no?