Please take care of all options that the spelling and numerical are correct and that the full-stops at the end where relevant are included. Please note that using other DNS names than those provided here might interfere with our ability to do seamless infrastructure upgrades in the future. Also, although you might get away with replacing the DNS names with their IP addresses, it is not compliant with DNS rules (MX records must not point to an IP address), as it will interfere with our ability to do certain kinds of infrastructure upgrades seamlessly. You can test your domain configuration using the tool provided on the EMP Cloud Interface.
Lastly, it is always recommended when changing DNS entries like MX records to lower the TTL (eg. to 600 or even 60 seconds) on the records well in advance of updating the entries itself. This allows the change itself to propagate in minimum time, and provides a quick way to revert the change should a test email indicate any unexpected problems. Usually, problems here are caused by forgotten firewall rules on the destination server. Once the change is made AND everything is working smoothly, the TTL should be changed back up to 86400 (or whatever it used to be… 86400 seconds = one day). These measures ensure maximum flexibility and minimum downtime should anything unexpected arise.