- No TLS — never use it.
- Opportunistic TLS — use it if it is available, if not, send insecurely.
- Forced TLS — use TLS or do not deliver the email at all
- Port 110 - this is the default POP3 non-encrypted port
- Port 995 - this is the port you need to use if you want to connect using POP3 securely
- Port 143 - this is the default IMAP non-encrypted port
- Port 993 - this is the port you need to use if you want to connect using IMAP securely
- Port 25 - this is the default SMTP non-encrypted port
- Port 465 - this is the port used, if you want to send messages using SMTP securely
- Port 578 - Authenticated SMTP
- RPC - this is the default SMTP non-encrypted port
Other related links
Exch 2013 ports
Exch receiver security settings
Outlook settings for POP and IMAP access for Office 365 for business or Microsoft Exchange