after mx record change emails still filtering to old exchange server

I have an exchange 2007 sitting with an older dc 2003 server. I had changed the mx records on Friday and it seemed emails have gone through. But then yesterday email started delivering back to the previous exchange. all mail records are correct double checked.

I had a mcafee spam server which I disabled. What else should I look for that can cause this issue. So users are working while others are not.

any ideas really appreciated.
Avi LeibzonAsked:
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matrix8086Commented:
from inside and from outside your organisation type this in cmd:

nslookup (press enter)
set type=mx (press enter)
your.domain (press enter)

Check what is listed on the screen if it is what are you expecting for

Best regards!
Avi LeibzonAuthor Commented:
both are the correct mx records.
Will SzymkowskiSenior Solution ArchitectCommented:
You need to make sure that you only have your new Exchange server NAT'ed on the firewall. If you have both Exchange servers listed it will route mail to both of them.

Will.

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Avi LeibzonAuthor Commented:
both helpful thanks.
backhaulCommented:
I feel I'd need A few things to review:
Things to consider:
Mail can still be delivered using an "A" record.
Bad DNS cache somewhere keeping your old record?

Other thoughts

Is the mail being received by the odd server coming from a few sites? Maybe those sites have a permanent forward to the old server.
The only way to solve this I feel is by looking at the mail header to get more information. Maybe email headers a few have something in common.
Avi LeibzonAuthor Commented:
thanks for the A record recommendation overlooked it, there was one record, that I changed. But mail has been going through well.
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