I have an issue where from select domains, occasional emails are being delivered several hours after being sent to us. We have an Exchange 2010 server with its anti-spam in place, Trend Micro's ScanMail 12 installed on the Exchange server, and a SonicWALL firewall. We have no cloud solutions in place. When I look at the message header info, all it shows is a time difference between when the sender sent it and Exchange received it. In most cases, the senders are not getting any type of delay message sent to them. As it is so sporadic, it is very hard to troubleshoot (as I can't automatically replicate the issue). I don't have any deep inspection/quarantine zones in place, at least not ones that would automatically release the email after some time. The header info usually shows that the SCL is 2 or less.
I'm hoping that someone can give me a suggestion or two as to where I need to look.
Any help will be greatly appreciated.