I have one link for you: 

http://portal.smartertools.com/KB/a240/configure-ssl-tls-to-secure-smartermail.aspx

The page above actually shows the best process to import your own self signed certs. I'll copy and paste it as well but I want you to know SmarterTools has a great knownledge base and support that goes beyond. 

I seem to have to look up the link once every year to renew some of my development certs.

Below is 100% SmarterTools KB talent. 

If the certificate has already been installed, you will find the private key in the computer's certificate store (aka, CAPSTORE). You will need to follow these steps to complete the process:

  1. Start | Run | MMC | OK 
  2. CTRL + M
  3. Click Add
  4. Select Certificates Click Add
  5. Select Computer Account
  6. Click Next then Finish
  7. Click Close and OK to get out to the MMC - now with two nodes.
  8. Click Local Computer>Personal>Certificate>mail.domain.org
  9. Right click select All Task then Export...
  10. Select Yes, Export Private Key
  11. Click Next, Next, Type a password, Next, Set filename to *.pfx select next and then finish
  12. Click Service>Personal
  13. Right click select All Task then Import...
  14. Select the pfx-file you just exported and follow the rest of the wizard throgh (Check Mark key exportable if you want).
  15. Finally, we need to export the certificate again for SmartMail. Click Local
  16. Computer>Personal>Certificate>mail.domain.org and select Export...
  17. Select No, do not export Private Key.
  18. Select Base 64 encoded X.509 (.cer) - IMPORTANT
  19. Set filename to mail.example.com.cer and save.
  20. Change security so everyone has read access on the cer-file
  21. Login as system administrator in SmarterMail
  22. Go to Security>Advanced>SSL
  23. Click New
  24. Specify your IP-address (matching the name on the certificate)
  25. Change to TLS (gives you better excptions in log-files)
  26. Specify a fully qualified file-name of you base 64 encoded X.509 cer-file.
  27. Save
  28. Restart SmarterMail Service.

SSL and TLS are two methods encrypting the session. SSL will encrypt the connection immediately upon connection. TLS will encrypt once the STARTTLS command is sent. This means that TLS can operate on the same default ports that SmarterMail is already utilizing!

SmarterTools KB shows you how to create your self signed certificate, import it and use it. Their instructions takes less than 2 minutes from your server to go from start to finish. I'm linking to them and have added the steps for myself here.