Am I crazy or is delivery to your old mailbox still possible after a migration?

[thecomputerguy]

I've noticed a few times after I migrate a client from wherever they are (ex. Rackspace) to O365 that sometimes current emails will get delivered to the old mailbox even though the MX & all required records have been changed to point to the new mailbox.

The current emails that get delivered typically come from the same person (ex. John A.) and the only explanation that I have for it is that John A has a live mailbox where the old mailbox now exists (ex. Rackspace).

Is it true that emails may be delivered internally if they exist at the same host provider and never hit the MX record?

The only way I've been able to fix this in the past is to delete the clients old mailbox on the old host. Either that or I'm going crazy, which is also equally as likely.

 

[ComputerRepairTech]

have to wait for dns propogation.

"Is it true that emails may be delivered internally if they exist at the same host provider and never hit the MX record?"
this is also true.

 

[thecomputerguy]

have to wait for dns propogation.

"Is it true that emails may be delivered internally if they exist at the same host provider and never hit the MX record?"
this is also true.

Yeah I'm not saying like hours after MX is changed I'm saying 3-5 days after MX was changed.

 

[nlinecomputers]

It can take as long as 72 hours for some servers to get the clue and update the local DNS records. Also, some email that might be automatically generated not use MX records but deliver to preconfigured IP addresses. (Stupid as that bypasses the whole point of MX records yet I've seen it happen.)

 

[GreyWolf]

I've seen this also but the way the problem was caused was the way servers we're routing the data for example here routes from Bell internet would go one way and Videotron cable would go the other so some would have the updated information others not usually takes a few days and all is ok. Lucky the occurrences are much more rare these days but like anything else nothing is perfect.

 

[SAFCasper]

If the person sending the email is also hosted with RackSpace that could be a possibility. Exchange online does something similar but I think only if the two addresses are in the same tenant.

My personal example:

I was migrating a client to Exchange Online. They have 2 domains so we decided to migrate them separately. DomainA went through without a hitch, everything working great.

So I start preparing DomainB. Added the domain to their 365 tenant and added all the mailboxes etc in advance ... but made no changes to DNS (other than to verify the domain) so it wouldn't be "active"

What happened? When they sent anything from DomainA to DomainB it went directly to the mailboxes in Exchange Online, which weren't supposed to be active yet. It just completely ignored MX records.

 

[Sky-Knight]

It's all DNS, there are many systems out there that just flat ignore DNS TTLs and go doing whatever they want with ancient data...jack you can do about it.

Typically those systems will forcibly update themselves when the old system stops responding.