We have an Exchange 2010 server which has been fully functional for a week.
This morning we found that some emails are not being sent but others are.
After more testing, some emails are going out but they are taking a good hour or so until they leave the queue.
I have run the Mail Flow troubleshooter and it tells me that there is no problem.
I have tried creating another send connector and using DNS instead of a smarthost but this has not worked either.
Server has also had a reboot and I'm out of ideas.
In the queue viewer it is not logging any error, emails are just simply sitting there.
I'm out of ideas!