Delayed Email to specific recipient

A sender from my domain A sends an email to a recipient on destination, domain B and cc's a member of sender's domain A.  The latter recipient receives the email immediately while the former shows a status of "transferred."  The email is sent at 4:31 PM and the recipient from domain B doesn't receive it until 5:30 PM.  The email has embedded images but is relatively small in size.

Now, I sent the same email from an external email account and it processed immediately to both recipients on domain A and B.  Then I forwarded the suspect email to my external account an received it immediately as well. I'm stumped.

Delivery report in Exchange shows

Delivery Report for ¿(¿
10/8/2013 4:31 PM mail1.domain.local
The message was submitted to mail1.domain.local.
10/8/2013 4:31 PM mail1.domain.local
The message has been queued on server 'mail1.domain.local' since 10/8/2013 4:31:25 PM (UTC-05:00) Eastern Time (US & Canada). The last attempt to send the message was at 10/8/2013 4:30:12 PM (UTC-05:00) Eastern Time (US & Canada).

10/8/2013 5:11 PM mail1.domain.local
Message delivery is taking longer than expected. There may be system delays. For more information, contact your helpdesk.

Then I checked SMTP logs but can't make much of them. They are on CST time so do I look in the log at the time recipient finally receives the email or when the sender sends it?

It does send eventually but an hour later.  Where else can I look to solve this mystery?
We have postini but it doesn't scan or touch anything outbound.

Thanks for any help.
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AmitIT ArchitectCommented:
Analyze the header information and check from which server it is taking maximum time.
ecosysAuthor Commented:
I can't grab the headers right now as the user is occupied. I will remote with him tomorrow to grab the email. He sent me an email but it didn't have headers.  I can say that I see it sitting in our Exchange queue for some time before it gets sent.
ecosysAuthor Commented:
There are no headers in our sent emails. I checked his and mine and am not seeing any.
ecosysAuthor Commented:
nevermind - I'm sorting with recipient. It seems to be an issue with their UK gateway.

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ecosysAuthor Commented:
I'm accepting my own comment for the solution because it is the closest thing to a solution.
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