A couple of problems I've found with the new version:

Mail list & preview - when an email is deleted the preview window still shows the contents of the deleted email, not the email that is now highlighted in the list.

View emails in plain text - when switched on some emails are not shown in the preview window, others are visible but still not shown in plain text.

Send email in plain text - doesn't work. I just tried it on one message and the message in the editing window still has the annoying grey line on the left of the quoted text. Plain text means plain text - no HTML.

And one from the old version that is still there:

Email aliases with commas in them, e.g. "Smith, John" - cannot be replied to unless the comma is manually deleted.