On Wed, Jan 09, 2013 at 01:29:06PM -0200, Rafael Azevedo - IAGENTE wrote:
> I was watching my log files now looking for deferred errors, and
> for my surprise, we got temporary blocked by Yahoo on some SMTPs
> (ips), as shown:
>
> Jan 9 13:20:52 mxcluster yahoo/smtp[8593]: 6731A13A2D956: host
> mta5.am0.yahoodns.net[98.136.216.25] refused to talk to me: 421 4.7.0 [TS02]
> Messages from X.X.X.X temporarily deferred - 4.16.56.1; see
> http://postmaster.yahoo.com/errors/421-ts02.html
Postfix already treats this as a don't send signal. Enough of these
back to back and transmission stops. This is a 421 during HELO,
not a 4XX during RCPT TO.
Yahoo's filters are NOT simple rate limits. They delay delivery when
their reputation system wants more time to assess the source. They
typically will permit delayed message when they're retried, unless
of course they believe the source to be spamming, in which case they
may reject, or quarantine...
> So guess what, I still have another 44k messages on active queue
> (a lot of them are probably to yahoo) and postfix is wasting its
> time and cpu trying to deliver to Yahoo when there's an active
> block.
> Yahoo suggests to try delivering in few hours, but we'll never
> get rid from the block if we keep trying while the block is active.
This is false. Postfix does not "keep trying" under the above
conditions, and Yahoo does not rate-limit in the naive manner you
imagine.
> This doesn't happens only with bulk senders. Many people use
> their hosting company to send few hundreds emails together with
> many other users sending legitimate mails from their mail clients?
> Eventually, one user will compromise all infrastructure and many
> people may have problem delivering their messages.
This is rarely a problem, and when it is, any blocking is usually
transient, and one can request to be unblocked, at most providers.
> There's gotta be a solution for this.
Yes, but not the one you're asking for. It is I think possible to
design and implement a useful dynamic rate delay algorithm, I am
not sure that spending the effort to optimize Postfix for unwhitelisted
bulk email is a good use of developer effort.
--
Viktor.
