When we resume Gmail sends, the front-loaded-inject + slow-drain pattern
buries mail: Listmonk stamps Date at injection (verified live: queued msg
Date matched postfix arrival, deferred 4h47m later), and Gmail sorts the
inbox by the Date header. So a msg injected at 08:00 but accepted at 14:00
files 6h down a Gmail inbox.
Documents: why NOT to future-date the Date header (spam signal + breaks our
DKIM which signs Date + doesn't help Outlook's received-time sort), and the
real fix -- pace Listmonk injection to match Gmail's accept rate (just-in-time
Date) via a dedicated Gmail stream on its own IP + low sliding-window rate +
queue-age guard. Outlook/M365 (current audience) sorts by received time so the
burial is cosmetic there and not worth fixing.
Procedure only; Gmail still excluded in _email_exclusions.py until re-enabled.
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