IMAP OR search beats client-side filter for fan-out
Surveying a large mailbox for threads matching multiple heuristics (sender domain plus body keyword) without downloading the whole mailbox.
To answer a question like "find every thread from an a16z domain OR mentioning a project name in the body", the obvious approach is fetch-then-filter — pull headers for every message in the folder and grep client-side. With 10k+ messages this is slow and pulls a lot of envelopes you do not need. The IMAP SEARCH command supports OR criteria server-side: imapflow accepts client.search({or: [{from: domain}, {body: keyword}]}, {uid: true}) and returns the matching UIDs in one round-trip. Even simpler: two parallel searches with different criteria (e.g. {from: domain} and {body: keyword}) plus Set-deduplication of the UID arrays client-side, then a single FETCH ENVELOPE pass over the union. On a 16k-message mailbox this took under 2 seconds vs minutes for the iterate-and-grep approach. ENVELOPE-only fetching (no BODYSTRUCTURE, no body) keeps the transcript small and avoids accidentally pulling PII you do not need.
When triaging a large mailbox via IMAP for multiple distinct match criteria, run one search call per criterion in parallel, dedupe UIDs client-side, then fetch ENVELOPE-only over the union — much faster than full-mailbox iteration and small-transcript-friendly.