I've set up a trial installation of WHM/cPanel on a Google Compute VM instance and it's considerably quicker (running and network response time) than my live WHM setup on a different and much more expensive dedicated server with RackSpace.
But (after a longish time digging) I find that Google don't allow their VMs to send mail on port 25.
https://cloud.google.com/compute/docs/tutorials/sending-mail
WHM Support say:
"If google VM is blocking port 25, there are no changes in WHM that will allow you to work around this. Exim MUST use port 25 to send/receive mail. The only other option would be to use a smart host, which would route the mail out through another server. This would require a second server configured for you to relay through it."
Is there another solution? Two servers would make my costs higher than they are now and lose one of the major benefits to me of moving to Google Compute from Rackspace.
Google Compute Engine customers can apply to Sendgrid free tier service that includes 25,000 transactional email messages per month .
Documentation for using Sendgrid on WHM/Cpanel with Exim is available here.
Sincerely,
Paolo