I know that a CNAME and a MX record can't exist on the same host. In this scenario I'm using A records to manage SMTP for 350 DNS domains.
companyA.com MX myAlias.whitelabel.com companyb.com MX myAlias.whitelabel.com companyc.com MX myAlias.whitelabel.com companyd.com MX myAlias.whitelabel.com
myAlias.whitelabel.com is an
A record. When you telnet to port 25 of that host, you will get a response from proofpoint saying a different host name:
220 mx0a-000a9001.pphosted.com ESMTP cm-m0074
Is there any validation of the SMTP host name against DNS?
Does the SMTP host name have to match the TLS certificate?
My goal is to simplify administration when I change the SMTP relay to another provider.