Is it possible to change extension of Altsync attachments?

Yes, you can change extension of Altsync attachments. Follow these steps:

1. Click Windows Start Button and enter %appdata% in the search field and click enter (alternatively click ctrl+r and type %appdata).
2. Go to Topalt\Altsync for Outlook and open config.xml with a Notepad.
3. Change the field <Extension>.zip</Extension>, replace .zip with your required extension.