Try to use IP address if no MX record?

[cxvqo]

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.

[link2xt]

You need to use IP address in the form of "alice@[127.0.0.1]" when sending.
Then you get an error "550: IP address literals are not supported":

maddy/internal/target/remote/remote.go

Lines 301 to 308 in b08b263

	if strings.HasPrefix(domain, "[") {
	return &exterrors.SMTPError{
	Code: 550,
	EnhancedCode: exterrors.EnhancedCode{5, 1, 1},
	Message: "IP address literals are not supported",
	TargetName: "remote",
	}
	}

This is still an issue, Postfix supports IP address literals and can send to them apparently, but maddy does not.

Also not having MX on a domain when sending to the domain should not prevent sending. The default is to use A record of the domain indeed, just no MX record should not prevent sending to the domain, this is what null MX is for.