i have an html email with this sentence 'xycfe11cg64d_2501034012' within the body of the message.
no result found when i search for '2501034012'
i have even tried using '*2501034012*' (wildcard)
Notmuch doesn't support regular expressions ("wildcards") when searching the body of messages, see the man page for `notmuch-search-terms`. It computes stems of words and indexes (and searches) those.
Using xapian commands, one could extract all stems and grep those for a term which one "remembers partially" (often happened to me), and then feed that into notmuch. Might be worthwhile scripting or even integrating into notmuch (sexp?).
Michael