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.