Re: Forwarders' hopes, was SPF and bouncing

At 11:01 08/04/2012  Sunday, Alessandro Vesely wrote:
>On Sun 08/Apr/2012 11:36:31 +0200 alan wrote:
>> At 15:05 07/04/2012  Saturday, Michael Deutschmann wrote:
>>>
>>> We aren't discussing forwarders, but ordinary SMTP with only one
>>> hop across the border.
>
>I like how SPF works in those cases.
>
>>> The only sustainable hope for a forwarder is a side deal with the
>>> admins of the ultimate recipient server to obtain the same
>>> super-whitelisting (overriding even mailbox diskspace quota and
>>> immune to automated blacklisting) that backup MXes have.  Then it
>>> really doesn't matter what the MAIL FROM: is.
>
>What about "generic" forwarders?  I mean sites who provide a web-form
>to let users specify whatever address they like.  They are obviously
>not going to hound ultimate servers' admins in order to have their
>site whitelisted.  BTW, most target domains are gmail, yahoo, and the
>like, so such whitelisting is probably tantamount a whitelist of all
>legitimate mail servers, which is probably what those huge mailbox
>providers are doing anyway.

we do the web form provision, we set envelope sender to account-identifier@our-domain 
(so sfp pass)
and bounces to this are re-written to the owner of the site
site owners who use hotmail or gmail are required to setup their hotmail/gmail to pickup their mail by pop3 rather than have us forward it to them

>Small to normally large mail sites cannot be reliable forwarding
>targets if they reject when an smtp.mailfrom results in a fail.
>So, I think it would be fair to require to also check smtp.helo in
>such cases, and accept the message if the it results in a pass.  What
>do you think?

most site owners on small sites have the ability to just whitelist their webservers (our servers) sending ip, those that arnt able to usually have to setup some sort of pop3 pickup if their mailsystem dosnt allow reliable forwarding 

>> ok this is the one time bounces MAY legitimately occur (disk
>> quotas) but unless the user side is abandoned or badly run it
>> shouldn't be persistent or even a common enough occurrence to cause
>> trouble (also sys-admins are supposed to be aware of these issues
>> to lart/delete the user before these issues happen) (as far as I am
>> aware no backscatter RBLs consider mailbox full as a listing
>> offence even if to innocent 3rd party due to this) a well setup
>> forwarder or frontline MX will cache 5xx and 2xx responses for
>> period (thus a 5xx from overquota) will result in 1 bounce every
>> period ONLY) obviously it also extends the period the forwarder or
>> frontline MX rejects incoming mail beyond the time the user has
>> resolved the issue, in our case 15mins as we see most users pickup
>> their mail at this interval.
>
>After a given number of bounces, the forwarding could well be removed.
>That's the approach mailing lists do, and provides for automatically
>removing stale addresses.  Are there implementations doing so?

well ours dosn't auto remove we rely on the admin being awake (but they are)
so they notice when it happens and call/im/txt the end user but if no response to extended mailbox full we will just manually disable the incomming address 5xx