IMAP4rev1 Clients (see also server comparison table)
client IMAP Standard Extensions (* marks in-progress extension)  
  SEARCH STARTTLS SASL SSL (ref?) SASL-IR ESEARCH NAMESPACE IDLE MULTIAPPEND UIDPLUS LITERAL+ CHILDREN SORT* THREAD* Lemonade More info
Apple Mail 2.x No Yes
(except port 993)		 No Yes
(port 993 only)		 ? ? ? No (but a plugin is available) ? ? ? ? ? ? ?
Apple Mail 3 Yes Yes GSSAPI, CRAM-MD5, PLAIN, LOGIN, NTML Yes No No Yes Yes No Yes Yes No No No No
Infotrope Polymer Yes Yes CRAM-MD5, PLAIN, ANONYMOUS, DIGEST-MD5 Yes [2] Yes Yes Yes [1] Yes Yes Yes Yes Yes [3] No No full profile
Microsoft Outlook No ? ? ? ? ? ? Yes ? ? ? ? ? ? ?
Microsoft Entourage 2004 Yes No ? Yes ? ? ? Yes ? Yes ? ? ? ? ? More info
Microsoft Entourage 2008 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
Modest Yes Yes (which mechs?) Yes ? Yes Yes Yes
(distinct session used)		 No ? Yes Yes ? ? Yes
(CONDSTORE/QRESYNC supported)
Mozilla Thunderbird Yes Yes PLAIN, CRAM-MD5 Yes ? No Yes Yes No ? ? ? No No ?
Mulberry Yes ? ? ? ? ? Yes ? ? ? ? ? Yes Yes ?
Mutt header, text, body Yes Cyrus SASL2
GSSAPI, CRAM-MD5, PLAIN, LOGIN, ANONYMOUS, DIGEST-MD5 		Yes ? ? ? Yes ? ? ? ? ? ? ?
Pine / Alpine Yes Yes GSSAPI, CRAM-MD5, PLAIN, LOGIN, EXTERNAL Yes No No Yes No Yes Yes No Yes Yes Yes No
(under consideration)
Plan 9 upas/fs No No ? Yes (port 993 only) ? No No No No No No No No No ? upas/fs
Your client here ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

[1] [Polymer] NAMESPACE support has a bug, exposed by the UW-IMAP's handling of the MH inbox, where the prefix is NIL.

[2] [Polymer] SSL support is pretty shaky. It's there, but quite possibly not fully working. The real problem is that Polymer cannot easily figure out a URL for message parts, and BURL servers cannot handle them anyway.

[3] [Polymer] And LISTEXT/LIST-EXTENDED CHILDREN return option.