Please follow the detailed instructions with screenshots below for setting Apple Mail 3.x up to work with turboSMTP server.

1. Open Apple Mail.
2. Click 'Mail', and then select 'Preferences...'
   
   
3. Open the 'Accounts' tab.
4. Click the 'Server Settings' button.
   
   
5. In the 'Outgoing Mail Server' box, enter pro.turbo-smtp.com
   

Then:

1. Make sure that 'Use Secure Sockets Layer (SSL)' is disabled.
2. Leave default SMTP Port 25.*
3. Choose password in the 'Authentication' section.
4. In the field 'User Name' type your Consumer Key (see how to create your API Keys).
5. In the field 'Password' type your Consumer Secret.
   
   
6. Click the 'OK' button.
   
   

*IMPORTANT NOTE

Many ISPs are now blocking traffic on default SMTP port 25. To avoid this restriction you can:

1. Change your turboSMTP port to 587 or 2525.
2. Enable SMTP secure authentication (SSL) and use port 465 or 25025.
   
   

Be sure that your firewall is not blocking these ports.