There's multiple ways, I'll cover a few of the popular methods.

First method is through WHM, on left hand side find the link that says Manage Mail Queue

The second method, which is the method I use, is to type this as root:

exim -v -qff &


The above method is very verbal, if you prefer not to hear any details, use:

exim -qff



If you want to just send one piece of email in the mail queue, use this command:

exim -M 11O3z-00042J-00


Replace 11O3z-00042J-00 with the message ID, which you can find by using this command:

exim -bp


To find only how many messages are in queue, you can use the following

exim -bpc


And lastly, to inspect the contents of a queued message to determine if it's spam, you can type:

exim -Mvl 123H3N-0003mY-00

This command would show you the contents of the message with the message ID 123H3N-0003mY-00