IMAP4 Keywords are small bits of metadata that can be attached to stored email messages.
They're free-form text, but the convention is that
\indicates a system keyword$indicates a keyword with a common meaning
See the IMAP4 spec and the IANA registry
| Keyword | Status | Notes |
|---|---|---|
| \Seen | System Required | |
| \Answered | System Required | |
| \Flagged | System Required | |
| \Deleted | SystemRequired | |
| \Draft | System Required | |
| \Recent | Deprecated | Not a user-set keyword |
| $MDNSent | IANA registered | in IMAP RFC |
| $Forwarded | IANA registered | in IMAP RFC |
| $SubmitPending | IANA registered | |
| $Junk | IANA registered | in IMAP RFC |
| $Phishing | IANA registered | in IMAP RFC |
| $Important | IANA registered | |
| $MailFlagBit0 | Apple Mail | Keywords combine to represent flag colours |
| $MailFlagBit1 | Apple Mail | |
| $MailFlagBit2 | Apple Mail | |
| $label1 | Thunderbird | Label names are stored internally and not on server |
| $label* | Thunderbird | |
| Junk | Custom | Deprecated in 2010, replaced by $Junk |
| NotJunk | Custom | Deprecated in 2010, replaced by $NotJunk |
| JunkRecorded | Custom | Is this Apple Mail? |
| Redirected | Custom | |
| unknown-0 | Custom | Missing tag information in Dovecot |
| OIB-Seen-* | Custom | OtherInbox service? |