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Changed hosted exchange providers but some mail still going to old boxes

We recently changed our name servers to point to Office 365 from an old hosted exchange server (over 72 hours ago).

We are noticing though that some mail is still being delivered to the old boxes...

We updated the name servers at our registar to point to the office 365 servers, and most new mail is arriving on the 365 server, but there still seems to be something strange.

Could it be propagation still??

If people on the internet respond to older messages from us (generated from the old server) will they route back to the old server? Could this be the issue?

Thanks,
Joe Cap
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jcaprio
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jcaprio
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1 Solution
 
Alan HardistyCommented:
Some servers don't use MX records to send mail and other take ages to update themselves.

If you switched MX records to Office 365 - close inbound port 25 and then the mail that is arriving in the wrong place, won't be able to.

If people on the internet respond to older messages from us (generated from the old server) will they route back to the old server?  No - not possible.
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jcaprioAuthor Commented:
but does that mean that the sender will receive a bounce back if I close port 25? and what about other pop/smtp accounts like gmail that user have set up in outlook? I do not want to block that traffic...
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Alan HardistyCommented:
No - port 25 inbound allows other mail server to SEND mail to your server.  As you no longer want mail delivered to your server, close the port.

Anyone sending mail directly to your servers and not using the MX records (which are usually spammers), will eventually realise you don't accept mail there and lookup your current MX records and use those (as they should do).  No NDR will be sent unless they can't send mail for several days to any mailserver.

GMAIL / POP account will collect mail from external sources, so closing port 25 inbound will have no bearing on those accounts at all.
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jcaprioAuthor Commented:
ok, so if we were using a hosted solution I would have to contact that company to do this, correct?

Or is this something we do on our router?
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Alan HardistyCommented:
If you are using a hosted solution, then you need to remove the mailboxes from that solution - they won't block port 25 for you.

Once the mailboxes are removed, then no more mail will arrive there.

It is possible that mail is arriving from companies using the same hosting provider (so it is seen as internal mail), which would explain why it isn't using your MX records to direct the mail.

Alan
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jcaprioAuthor Commented:
there was a forward from another domain that was causing the issue. Resolved.
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jcaprioAuthor Commented:
Solved it on my own
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