Under "Outgoing Mail Server", select the checkbox for "My
server requires authentication".
Apply Secure Sockets Layer (SSL)
Select the Advanced tab.
Under "Server Port Numbers", below "Outgoing Mail (SMTP)", select the checkbox for "This server requires a secure connection (SSL)". Set the SMTP port to 465. Note that if you are not able to send mail, change this setting to port 587; this will force Outlook to negotiate its secure connection with the email server.
Below "Incoming Mail", select the checkbox for "This server requires a secure connection (SSL)". The ports will automatically change to 995 for POP3, and 993 for IMAP.