Support SMTPS

[lenovouser]

wikipedia.org/wiki/SMTPS

• Port 587 → STARTTLS
• Port 465 → TLS

Might fix #7, generally this library has been wrongly reporting invalid mailbox for a lot of domains that don't offer plain SMTP for me

[lucacanella]

Same for me. I manually tested one of my email addresses and it failed the SMTP validation just because the mail server accepted secure connections only (also port 25 was timing out since plain SMTP was not supported) .