Email: Replace «Use SSL» checkbox with dropdown.

[oddstr13]

Mailkit (the underlying library) supports five different encryption stratergies;

• No encryption
• Attempt encryption (auto, fall back to none)
• SSL (enforce SSL, otherwise fail)
• StartTLS (enforce StartTLS, otherwise fail)
• StartTlsWhenAvailable

https://mimekit.net/docs/html/T_MailKit_Security_SecureSocketOptions.htm

See #258 for some additional discussion around this.

For comparison, Thunderbird provide the following configuration options:

• None
• STARTTLS
• SSL/TLS

The auto behavior(s) are in my opinion best suited for connecting to «unknown» email servers for direct delivery (not really something you do today, due to spam issues), as opposed to connecting to a relay.