Try to use IP address if no MX record?

Currently, when trying to either use an IP address as the domain for an email address, or a domain without an MX record, it returns: `SMTP error 554: MX lookup error`
Could there be an option to try to send to the IP address directly?
(This seems to work in Outlook, for compatibility's sake?)

It would be useful for local email communications, maybe the mx-less domain part less, but it'd still be useful, it would make sense for this to be disabled by default.