Checks whether a single email address is deliverable. Exits successfully if so.
To install:
$ go get github.com/ransford/vrf
Is foo@bar.quux a deliverable email address?
$ vrf foo@bar.quux
foo@bar.quux is deliverable
$ vrf -quiet foo@bar.quux && echo "yes"
yes
What about oiwperwer@google.com?
$ vrf oiwperwer@google.com
oiwperwer@google.com is not deliverable
$ vrf -quiet oiwperwer@google.com || echo "no"
no
vrf looks up the mail exchanger (MX) records for a given address, then
connects to the highest priority server in the list and goes partway through
the process of delivering an email messsage. Essentially:
> Client: Hello `domain.com` mail server!
> Server: Hello!
> Client: I have email for user `bob@domain.com`.
> Server: Sure, I'll accept it. ***OR*** Sorry, no such address.
> Client: Never mind.
> Server: Fine, whatever.
> Client: Bye!
> Server: Bye.
Technically speaking, vrf disconnects (politely, with RSET) after MAIL.