Hi,
In regards to your issue, you can use Powershell to add CNAME RR in DNS server to set TTL. But you have to add a MX record must be created under domain name that you are using as the email address suffix.Secondly, you can create an CNAME record in the DNS server.
Open Powershell> Run as administrator> Type the following commands:
Add-DnsServerResourceRecordMX -Name “MX_NAME” -MailExchange “vglgum624VM.lab.com” -ZoneName “lab.com” -TimeToLive 10:10:10
Add-DnsServerResourceRecordCName -Name "CNAME_NAME" -HostNameAlias "vglgum624VM.mail.lab.com" -ZoneName "lab.com" -TimeToLive 10:10:10
I have tested in my environment and it works.
For more details, you can refer to the following link:
https://video2.skills-academy.com/en-us/powershell/module/dnsserver/add-dnsserverresourcerecordcname?view=win10-ps
https://www.mustbegeek.com/add-mx-record-in-windows-dns-server/#.XyjG9ygzaUk
If my answer is helpful to you, please remember to mark them as answer. Thank you!
Best regards,
Gloria