When I updated to v.4, it erased all my data, so I had to import the .xn file. The problem is that the passwords do not work. I had to re-enter most of the passwords to get it to check them. None of the PWs had changed, they simply did not work with the new version.
I'm back to 3.5.23 for now, because I like the one-click to open all emails that have new messages. I hope this can be worked out in the future on newer versions.
Import .xn with 3.5.23
To use 4.0 Import with 3.5.23 and save it is how this works for me.