You set up authentication in the mail accounts. Extras > E-Mail-Accounts, edit existing account. Then pick an account from your list, choose Properties, Advanced Properties, and edit the authentification settings accordingly. There is no designate authentication tab, but various authentication options are spread throughout the settings dialog.
* Under "Outgoing Mail Server" you can set smtp authentication.
* Under "Enhanced" you can set SSL settings.
Most mail servers will require AUTH LOGIN, which means that username and password need to be sent base64-encrypted before sending mail to a foreign domain is possible. There is an easy way to check this.
1. Open Command Prompt.
2. Type: telnet <your smtp server> 25
3. Telnet will open up. Enter EHLO <your domain name>.
4. It will show you what authentification methods are supported.
Here's an example:
250-smartmx-10.domain.com Hello domain.com [192.168.0.1]!
250-SIZE 31457280
250-PIPELINING
250-AUTH PLAIN LOGIN
250-STARTTLS
250-HELP
As you can see, in this fictional example, the mail server supports authentification via plain text and login. Plain text means that username and password are sent in unencrypted form. Usually this is a bad idea as it's insecure. Login means that username and password need to be in base64 encrypted form.
As a final note, the EHLO command usually displays much more internal information about your mail server that can come in handy. The SIZE command shows you the maximum mail size the mail server will send, in bytes. There are other things to find out as well, best if you search google for that, in case you ever need it.
