The SMTP protocol is getting on in years and has often been pronounced dead, but now it seems to have been dealt its death blow. Exchange 2019 will no longer support SMTP. MAPIoverHTTP and EWS are waiting in the wings as successors.
The SMTP protocol for exchanging emails has been around since 1982, so it is only logical that a successor to the antiquated protocol needs to be found. Microsoft is getting its act together and will no longer support the old SMTP protocol with the upcoming Exchange 2019 version. In future, emails will be delivered to Exchange Server via MAPIoverHTTP or EWS. However, moving away from SMTP as the standard protocol for mail traffic is not without its hurdles, as there are a number of requirements that need to be met:
- Correct autodiscover configuration (so that other mail servers can determine the mail server via MAPIoverHTTP or EWS)
- Correctly set certificates that contain all corresponding Exchange URLs
- Gateways that use SMTP as a protocol must be replaced
SPAM filters that do not support MAPIoverHTTP or EWS can therefore no longer be used with Exchange 2019. There is therefore a lot for administrators to do here: Applications and services that previously relied on SMTP need to be updated or replaced. SPAM filters need to be replaced and many scripts will probably need to be adapted.
However, there are also advantages: MX records are no longer required.
PS: Today is April 1. 
