Disclaimer: Updated when I feel like it, correct as I like it. In most cases, information is taked from https://codesearch.debian.net.
The table for servers support can be found on imapwiki: https://www.imapwiki.org/Specs
Capabilities list taken from related IANA registry at 2019-06-01. Obsolete extensions are not included.
A client is considered to support extension if it checks its support on the server by looking at returned capabilities list. Even if it doesn't actually makes any use of it.
Legend: ? - unknown (probably doesn't support), + - supports, - -
doesn't support (check git blame for update timestamp)
| Capability Name | Thunderbird | KMail | Roundcube | Rainloop | mutt | balsa | geary | Evolution |
|---|---|---|---|---|---|---|---|---|
| ACL | + | + | + | - | + | + | - | - |
| ANNOTATE-EXPERIMENT-1 | - | - | - | - | - | - | - | - |
| APPENDLIMIT | - | - | - | - | - | - | - | - |
| BINARY | - | - | + | - | - | + | ? | ? |
| CATENATE | - | - | - | - | - | - | - | ? |
| CHILDREN | + | - | - | - | - | + | + | + |
| COMPRESS=DEFLATE | + | - | - | - | - | + | - | - |
| CONDSTORE | + | + | + | + | - | - | - | + |
| CONTEXT=SEARCH | ? | ? | ? | ? | ? | ? | ? | ? |
| CONTEXT=SORT | ? | ? | ? | ? | ? | ? | ? | ? |
| CONVERT | ? | - | - | - | - | - | - | ? |
| CREATE-SPECIAL-USE | - | - | + | - | - | - | - | ? |
| ENABLE | + | - | + | - | + | - | - | ? |
| ESEARCH | ? | ? | ? | ? | ? | + | ? | ? |
| ESORT | - | - | - | - | - | - | - | ? |
| FILTERS | ? | ? | ? | ? | ? | ? | ? | ? |
| I18NLEVEL=1 | - | - | - | - | - | - | - | ? |
| I18NLEVEL=2 | - | - | - | - | - | - | - | ? |
| ID | + | ? | ? | ? | ? | ? | ? | ? |
| IDLE | + | + | - | - | + | + | + | + |
| IMAPSIEVE= | - | - | - | - | - | - | - | - |
| LANGUAGE | - | - | - | - | - | - | - | - |
| LIST-EXTENDED | + | ? | + | ? | ? | ? | ? | + |
| LIST-MYRIGHTS | - | - | - | - | - | - | - | - |
| LIST-STATUS | ? | ? | + | + | ? | ? | + | + |
| LITERAL+ | + | ? | + | ? | ? | + | ? | + |
| LITERAL- | - | - | - | - | - | - | - | - |
| LOGIN-REFERRALS | - | - | - | - | - | - | - | - |
| LOGINDISABLED | + | + | + | - | + | + | ? | - |
| MAILBOX-REFERRALS | - | - | - | - | - | - | - | - |
| METADATA | ? | + | + | - | - | - | - | - |
| METADATA-SERVER | ? | ? | + | - | - | - | - | - |
| MOVE | + | + | + | - | - | - | ? | ? |
| MULTIAPPEND | ? | ? | ? | ? | ? | + | ? | ? |
| MULTISEARCH | ? | ? | ? | ? | ? | - | ? | ? |
| NAMESPACE | + | ? | ? | ? | + | + | ? | + |
| NOTIFY | ? | ? | ? | ? | ? | ? | ? | + |
| OBJECTID | ? | ? | ? | ? | ? | ? | ? | ? |
| QRESYNC | ? | ? | + | ? | ? | ? | ? | + |
| QUOTA | + | + | + | + | ? | + | ? | + |
| REPLACE | ? | ? | ? | ? | ? | ? | ? | ? |
| RIGHTS= | ? | ? | ? | ? | ? | ? | ? | ? |
| SASL-IR | ? | + | + | + | + | + | + | ? |
| SAVEDATE | ? | ? | ? | ? | ? | ? | ? | ? |
| SEARCH=FUZZY | ? | ? | ? | ? | ? | ? | ? | ? |
| SEARCHRES | ? | ? | ? | ? | ? | ? | ? | ? |
| SORT | ? | ? | ? | ? | ? | + | ? | ? |
| SORT=DISPLAY | ? | ? | ? | ? | ? | ? | ? | ? |
| SPECIAL-USE | + | ? | + | + | ? | ? | + | + |
| STARTTLS | + | + | + | + | + | + | + | + |
| STATUS=SIZE | ? | ? | ? | ? | ? | ? | ? | ? |
| THREAD | ? | ? | ? | ? | ? | + | ? | ? |
| UIDPLUS | + | + | ? | ? | ? | + | ? | ? |
| UNAUTHENTICATE | ? | ? | ? | ? | ? | ? | ? | ? |
| UNSELECT | ? | ? | ? | ? | ? | + | ? | ? |
| URLFETCH=BINARY | ? | ? | ? | ? | ? | ? | ? | ? |
| URL-PARTIAL | ? | ? | ? | ? | ? | ? | ? | ? |
| URLAUTH | ? | ? | ? | ? | ? | ? | ? | ? |
| UTF8=ACCEPT | ? | ? | ? | ? | + | ? | ? | + |
| UTF8=ONLY | ? | ? | ? | ? | + | ? | ? | + |
| WITHIN | ? | ? | ? | ? | ? | ? | ? | ? |