The imap server software has been upgraded (slightly!) to log logins that were made via TLS or SSL as such. UW-IMAP would log SSL-initiated connections, but wouldn't log connections that were TLS-negotiated.
Messages look like this, for an encrypted login attempt (either TLS or SSL)
Dec 6 09:39:37 mr4 imapd[16487]: Login (SSL) user=travel host=accounting-3.finsrv.umbc.edu [130.85.165.232]
or
Dec 6 09:48:00 mr4 imapd[16983]: Login (CTX) user=banz host=kyle.ucs.umbc.edu [130.85.70.249]
for a clear-text authentication.