Another tip for domains that don't send email: set a null mx record. This explicitly tells sending servers that your domain does not receive mail, and isn't just broken. Create an mx record priority 0, with a dot (.) for the value.
I'd like to add that this is because with no MX record the MTA may still attempt to deliver email to the IP from the domain A/AAAA record.
This is a lesser known feature of SMTP, it is specified in rfc5321 section 5:
If an empty list of MXs is returned,
the address is treated as if it was associated with an implicit MX
RR, with a preference of 0, pointing to that host.
>Another tip for domains that don't send email: set a null mx record. This explicitly tells sending servers that your domain does not receive mail...
Most of my domains don't send mail, however I do prefer to receive mail to the standard aliases (webmaster@, abuse@, etc) and often a catchall. Even for domains I've got parked and awaiting deployment.
Am I thinking too much, not enough, or is the opening phrase of the advice meant to be "Another tip for domains that don't intend to receive email"?
Oh wow, TIL. Does that work? It says the draft expired in 2014.
"[T]he SMTP client first looks up a DNS MX RR and if that is not found it falls back to looking up a DNS A or AAAA RR.
Many domains do not accept email, but do have A or AAAA records. If they have no MX records, senders will attempt to deliver mail to those A or AAAA records. "
Nothing like a good opt-out to make you feel like you're signing up to a Do Not Call list.
I guess we can't blame email too much, it's an incredibly old protocol. But at some point, some quirks have got to be worth rethinking, right?
Maybe we can deprecate the fallback from MX to A/AAAA for the next, oh I don't know, two hundred years before we can move on.
https://tools.ietf.org/id/draft-delany-nullmx-02.html