IMAP - retrieve mail by Yahoo X-YMailISG

Question

Appears for all incoming Yahoo mail, X-YMailISG is an incoming message ID mail can be retrieved by. I'm wondering if this is possible in IMAP or if this field is used for something else entirely?

Answer 1

From RFC 3501, section 6.4.4, you could use SEARCH or UID SEARCH with the HEADER qualifier to look look for the identifier for that message.

Quoted:

HEADER <field-name> <string>
         Messages that have a header with the specified field-name (as
         defined in [RFC-2822]) and that contains the specified string
         in the text of the header (what comes after the colon).  If the
         string to search is zero-length, this matches all messages that
         have a header line with the specified field-name regardless of
         the contents.