Hi Paul,
I got some issues understanding the mail flow in your situation. Just to
make sure:
world -> university -> o365 -> google
If the google-account was deleted/disabled, why would google generate an
MDF? The mail should be rejected by google, so not "leaving" o365? And I
would expect o365 to have procedures in place to handle it? How are your
servers involved at all?
On 16.10.2015 16:50, Osborne, Paul (paul.osborne@???) wrote:
> Hi,
>
> I have had a slightly odd situation where a member of the university
> (best leave it at that) has decided that they do not like our O365
> offering (which we treat effectively as a mail store) and decided
> that they wanted to forward their email to Google. This in itself is
> not a particular issue and worked fine.
>
> Then at some point their Google account was deleted (no idea why and
> don't really care) at which point the forwarder in O365 continued to
> forward email to Google which generated a MDF that came back with an
> ensuing game of email ping pong that resulted in us getting black
> listed for a time.
>
> Sadly due to address rewriting going on and new emails being
> generated for the forwards coming out of O365 (rather than a true
> message bounce) getting this spotted as a mail loop has proven to be
> a challenge.
>
> We do have sender rate limiting in place - however people higher up
> the food chain than me have insisted it is set the same as O365 to
> give parity of user experience. The downside of this is that O365
> rate limiting is apparently set to: 10,000 recipients per day and 30
> messages a minute. So pretty much low enough to be useless.
>
> https://technet.microsoft.com/en-gb/library/exchange-online-limits.aspx#RecipientLimits
>
> At this point I am thinking about implementing rate limiting on the
> basis of a sender being able to send X number of mails per unique
> recipient email address per day - to reduce the flow enough so that
> things start to back up a bit internally and my monitoring can spot
> when this happens.
>
> However looking at the rate limiting config in Exim although I can it
> seems limit the amount of recipients that a sender can mail to, I
> cannot see that I can limit the amount of mails that a user can send
> to individual recipients. It may be the case that I am failing to
> parse the documentation and for that I apologise, but if anyone has a
> suggestion on how to do this I would appreciate it.
>
>
> Cheers
>
> Paul
>
>
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