[Mailman-Users] Unexplained unsubscribes of yahoo.com email

Hank van Cleef vancleef at lostwells.net
Mon Mar 1 21:36:09 CET 2010

The esteemed Mark Sapiro has said:
> Very persistent as in delaying for more than 5 days, or is your MTA's
> retry period shorter than that?
> I'm sure you know what's happening in your case; maybe I'm just lucky,
> but I think my Yahoo deferrals/retries always succeed within way less
> than 24 hours.
> <rant>
> I think Yahoo is wrong in this. If the deferrals are a form of
> greylisting, there's no point in deferring more than once. One delayed
> retry proves the sending MTA is going to retry and subsequent
> deferrals are pointless. On the other hand, if they're never going to
> accept the mail, they should reject it outright with a 5xx. The only
> result from deferring multiple times and then accepting is to cause
> problems for their users resulting from delayed mail and to waste
> network resources with all the unnecessary retries.
> </rant>
I recognize this pattern in dealing with several of the large
recipient sites.  Can't recall now, but I think yahoo, hotmail, and
verizon all pulled this stunt, and what's happening is not obvious to
the Mailman admin who does not have access to sender site logs.
I'm using sendmail as MTA, so this scenario is what happens with

Rather than bounce the mail with a 5.x.x DSN the recipient site defers
with a 4.x.x DSN.  Mailman, as an MUA, receives notices sent to
listname-bounces that the mail is being deferred, but unless Mailman
is set to deliver those messages to the admin, they vanish.  

The MTA has a timeout (sendmail default is 5 days, I reset to 3) after
which it discards mail from the queue and sends a bounce message,
which gets processed.  After receiving bounces for N days, Mailman 
sets the address nomail-by-bounce.  It becomes obvious to the Mailman
admin when the bounce processor sends the bounce notices.  Generally,
the bounce reminders also get blocked by deferral, so Mailman
unsubscribes the acount after the waiting period.

To put the frosting on the cake, the recipient doesn't get the "you've
been unsubscribed" message, either.

In a couple of cases, the bounce messages sent to the sendmail log 
will start having http links in the message.  Only the site
administrator who is reading the MTA logs gets to see that, and it's
sporadic---not every deferral message has that included.  The link is
generally to a URL for getting the sender site whitelisted with the
big mail operation.

Needless to say, the whole thing is pretty invisible to both a Mailman
administrator and the recipients.  In the meantime, the MTA queues get
filled up, the addresses get retried at regular intervals.  Consider 5
days of deferrals before the first bounces to Mailman, three more for
Mailman to set the user nomail, then three more weeks to the
unsubscribe.  And of course, the days of deferrals and retries make
the mail list look like a spam generator.

We're set up here to discard unrecognized bounce messages (that
address is a prime spam target), but to get bounce and unsubscribe


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