AbstractSmtpTransport::_isFqdn() let's wildcard hostnames pass -> SMTP error

[tolry]

Hi,

when using nginx with a wildcard server entry like
server_name *.mydomain.de
this server-name ist passed to AbstractSmtpTransport::_isFqdn() which accepts this as an fqdn entry and uses it as HELO. Which in return will fail on most MTAs (e.g. exim4).

I will try and prepare a PR in the next few days.

kind regards,
Tobias

[tolry]

#302 has already "a" solution, but probably not the best