Forum Discussion
Clarifications on MTA-STS Policy with CNAME Records
TechCommunity and The_Exchange_Team, In the article "Introducing MTA-STS for Exchange Online," there's a statement: The_Exchange_Team wrote: We do not support CNAMEs when MTA-STS is used. If...
The way I read it is that they don't support having a CNAME record for an MX record when using MTA-STS