[gorm]

Nearly correct. You should also do a DNS lookup on $2 and check if it has either a MX record or an A record before trying to send it.

[hn_throwaway_99]

FWIW the linked library does that, https://github.com/dominicsayers/isemail/blob/master/is_emai...

[gorm]

It looks like it only check for a MX, but email could might be delivered with just an A record and without a MX record I think.