The ONS email server implements the following standard email protocols:

POP3 (TCP port 110) and POP3/SSL (TCP port 995)

IMAP (TCP port 143) and IMAP4/SSL (TCP port 993)

SMTP with AUTH LOGIN, AUTH CRAM-MD5, and TLS (TCP port 25)

Both IMAP and SMTP support STARTTLS

If you operate from some remote locations that use a proxy firewall, you may be unable to connect to the SMTP server on TCP port 25 with a secure connection. In this case, you should use SMTP/SSL port on TCP port 465.

Important! POP3 and IMAP do not encrypt the data stream and are not recommended because they are vulnerable to connection eavesdropping.  This can expose your password and the contents of your emails to third parties. This exposure is critical if you are accessing your server's email functions from a wireless network or from a remote location.  Instead, we strongly recommend that you use IMAP/SSL and SMTP/TLS.  To do this in Microsoft ®Outlook and friends, just check the box "This server requires a secure connection" in the advanced tab of account setup for both SMTP and IMAP/POP3.

The IMAP protocol is a superior way to retrieve your email as compared to POP3. If you retrieve your mail with POP3, it creates some problems if you use more than one computer to check your mail. IMAP is both faster and more reliable and is ideal for users that have both a desktop computer and a laptop.

If you use your computer both in the office and on the road, you should select the options for "This server requires authentication" and "Use the same settings as my incoming mail server." Otherwise, you will not be able to send email from a remote location.  This prevents your email server from being an "open relay" that might be used by spammers.

For all the details about all Internet protocols, you can search and view all the Request for Comment documents (RFC's) at the RFC repository maintained by the The Internet Engineering Task Force