TEXT <string>
Messages that contain the specified string in the header (including MIME header fields) or body of the message. Servers are allowed to implement flexible matching for this search key, for example, matching "swim" to both "swam" and "swum" in English language text or only performing full-word matching (where "swim" will not match "swimming").
It seems not, or maybe just for subject/from/to fields ?
Please specify which RFC's and functionality Zoho Mail implements for IMAP search. Thanks.