Right now, I send mail via a Windows server. It has MailEnable, and I've customized it.
Sending email on it is better than cPanel, because it has both DomainKeys and DKIM. And the DKIM is 1024-bit, higher than cPanel's 768 that's officially deprecated. Beyond that, all of my records -- DNS, FBLs, etc -- are tied to that IP. I'd just assume leave it alone. It works great.
Receiving email, however, is not so great. The filters in cPanel are simply better. And sometimes, about once per month, the MTA/SMTP also gets hung up for inbound, and I have to manually restart the service. IMAP also works better on cPanel.
This should be fine, but I wanted to double-check with others. The DNS records all appear to be for sending emails. I want to keep the same mx -- "mail.mydomain.com" -- which would then go to the cPanel server. I always send via IP anyway, for the Windows server SMTP.
I plan to test this out with an unused domain on the server.
Sounds OK. Only thought I have is that a few receiving servers might have been set up with crude / over-strict settings, assuming that valid outbound email for the address would only come from the same server the MX record points to (ie not "proper" spf/dkim).
Hopefully not many, and it's really up to them to change their settings, but frustrating if it affects you or your customers.