When a client connects to port 143 and is configured to issue a `STARTTLS` command, #Guam responds with a `CAPABILITY` response that is the configured backend's response either after implicit SSL (doesn't contain `STARTTLS`) or explicit `STARTTLS` (doesn't contain `STARTTLS` either).
The client however requires a `CAPABILITY` response with `STARTTLS` (probably a minimal `CAPABILITY` response):
```
$ imtest -t "" -u vanmeeuwen -a vanmeeuwen kolab.kolabsys.com
S: * OK [CAPABILITY IMAP4rev1 LITERAL+ ID ENABLE STARTTLS LOGINDISABLED] kolab02.kolabsys.com Cyrus IMAP 2.5.5.5-Kolab-2.5.5-5.1.el6.kolab_14 server ready
C: S01 STARTTLS
S: S01 OK Begin TLS negotiation now
verify error:num=19:self signed certificate in certificate chain
TLS connection established: TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)
C: C01 CAPABILITY
S: * CAPABILITY IMAP4rev1 LITERAL+ ID ENABLE ACL RIGHTS=kxten QUOTA MAILBOX-REFERRALS NAMESPACE UIDPLUS NO_ATOMIC_RENAME UNSELECT CHILDREN MULTIAPPEND BINARY CATENATE CONDSTORE ESEARCH SORT SORT=MODSEQ SORT=DISPLAY SORT=UID THREAD=ORDEREDSUBJECT THREAD=REFERENCES ANNOTATEMORE ANNOTATE-EXPERIMENT-1 LIST-EXTENDED LIST-STATUS LIST-MYRIGHTS WITHIN QRESYNC SCAN XLIST XMOVE MOVE SPECIAL-USE CREATE-SPECIAL-USE URLAUTH URLAUTH=BINARY X-NETSCAPE AUTH=PLAIN AUTH=LOGIN SASL-IR COMPRESS=DEFLATE X-QUOTA=STORAGE X-QUOTA=MESSAGE X-QUOTA=X-ANNOTATION-STORAGE X-QUOTA=X-NUM-FOLDERS IDLE
S: C01 OK Completed
Please enter your password:
```