Valid e-Mail adresses are hard to verify. Do not do it.

These email adresses are valid:
@1st.relay,@2nd.relay:user@final.domain
relay.domain!user@domain
user%final.domain@1st.relay
'*+-/=?^_`{|}~#$@netmeister.org
"🍺🕺🎉"@domain
jschauma@شبكةمايستر..شبكة
santa.cl@ws
jschauma@[IPv6:2001:470:30:84:e276:63ff:fe72:3900]