Exchange - emails with attachments are being delayed to server

We are running Exchange 2007 on Windows SBS 2008.

We are experiencing large lags in delivery times from emails sent from gmail and comcast. I have been doing
a lot of testing and this is what I am experiencing.

One gmail account can send emails of any size up to the limit dictated on the exchange server and they
are delivered promptly.

Another gmail account can send an email with a very small attachment (100KB) and it will go right through,
but an attachment that is 1MB or larger takes a long time to arrive, perhaps 20 minutes or hours.

The same happens with a comcast email account I tested with where it takes the larger file forever to arrive.

I checked the header and there was a different route the email took for the larger emails and the emails would be
held up at a hop before reaching us, sometimes 1 sometimes 2 hops before depending on the provider. This pointed to
MX records for me. I checked and sure enough there was a bad MX record weighted at 10 with an MX record that was good
that was also weighted at 10. I had a backup MX record weighted at 20 that pointed to a different A record, but the
same valid IP as the good 10 record. This further suggested to me that the bad MX was out there on certain routers.

I cleaned up the MX records at least 36 hours ago and I was pretty sure this would take care of the issue. Unfortunately, the same
behavior is happening. I also realized that a new reverse DNS record was never set up, but that should have nothing to do with this
type of behavior.

Could it be anything else or could it actually take this long for all of the MX records to be updated across the internet?

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mjsheppard74Connect With a Mentor Author Commented:
It wasn't DNS, there was something with the firewall possibly causing issues with an old configuration. It was a checkpoint - safe@office 225. I had to restore it to the default settings and then reconfigure it. This solved the issue.
Cris HannaCommented:
All DNS records can take 48-72 hours to populate world wide.   Depends on the settings of the DNS server how often they refresh their records...Also depends on your Web hosting company's DNS server settings as to how long their servers are set for TTL
On Saturday...I would consider checking records with multiple free DNS tools   ie mxtoolbox  dnsstuff and so on.
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