You need to configure the client to use encryption. I think this is covered in the release notes, and has been mentioned here numerous times.
Using encryption ssl or startls is how we got Thunderbird to work -
You are right though Outlook Express now works with SSL enabled but "Do Not Log on using Secure Password Authentication" or it doesn't find the boxes.
Same issue with Thunderbird - use passwords required but do not use Encrypted Passwords.
Additional benefit - I just tried running Selective Restore of a full backup and it now shows. I could never do this with SME 7.5 so I assume the damaged mail file within a folder interfered with a full DAR Backup - as well a Full Dar Restore would not work. However as mentioned the Dar2 backup did work
I would advise anyone using Dar backups to see if they can do a selective restore - if they can not, then do not expect to be able to do a Restore.
Ken