Is IMAP CONDSTORE widely supported?
As I needed a more precise answer, I did a small node.js script and used some test accounts.
Here are the results, if you need more accounts, tell me.
yahoo
No CONDSTORE.
- IMAP4REV1
- ID
- NAMESPACE
- X-ID-ACLID
- UIDPLUS
- LITERAL+
- XAPPLEPUSHSERVICE
- XYMHIGHESTMODSEQ
gmail
CONDSTORE supported.
- IMAP4REV1
- UNSELECT
- IDLE
- NAMESPACE
- QUOTA
- ID
- XLIST
- CHILDREN
- X-GM-EXT-1
- UIDPLUS
- COMPRESS=DEFLATE
- ENABLE
- MOVE
- CONDSTORE
- ESEARCH
outlook.com
No CONDSTORE.
- IMAP4REV1
- CHILDREN
- ID
- NAMESPACE
- UIDPLUS
- UNSELECT
No, it is not widely supported. You can treat it as an optimization to use when available, but you cannot depend on it. You also need a way to track removed messages, which is not something condstore can tell you
Gmail, however, just rolled out support for it recently.