Recently, Gmail has started to rate-limit deliveries from our
mailing list server, with this message:
SMTP error from remote mail server after end of data: This mail
has been rate limited because it is unauthenticated. Gmail
requires all senders to authenticate with either SPF or DKIM.
According to https://support.google.com/mail/answer/81126 also:
Starting February 2024, Gmail will require the following for
senders who send 5,000 or more messages a day to Gmail accounts:
Authenticate outgoing email, avoid sending unwanted or
unsolicited email, and make it easy for recipients to
unsubscribe.
In order not to place undue additional load on our MTA's deferral
queue, adding a neutral SPF rule is nicer than unsubscribing and
blocking all Gmail users. A simple "a" rule should suffice, since we
don't relay through any smarthost currently. Set the TTL to 5
minutes for now, in case we need to make rapid adjustments to this
policy in the near future.
Change-Id: I388de615035156bc277ff1e1b11ac2bc0346cb27
05d1c26ee7