Add support for SMTP with SSL.

[airblade]

Fastmail requires SMTP to use SSL but not STARTTLS. This change enables
ones to turn on SSL without automatically starting TLS.

Here are some relevant links:

http://blog.fastmail.fm/2012/05/21/enforcing-ssltls-encryption-of-all-connections/
https://www.fastmail.fm/docs/encryption.html#ot

[ghost]

Would it make more sense to have a single option for this?

notify_by Mail do |mail|
  mail.encryption = :starttls # or :ssl (or :tls)

Setting Mail's :ssl or :tls option to true negates it's enable_starttls_auto setting.
Net::SMTP does not distinguish between :ssl or :tls, but having the option accept both might be easier for users following various email client setup instructions to understand.

https://github.com/meskyanichi/backup/compare/mail_notifier

What do you think?

[airblade]

Good idea – I agree.