Summary -------------- Pretty solid plugin, does the job, could have more polish (weird warning message grammar) and improved in a number of ways.
Detail -------- I have tested to being used to back up and restore an Outlook exchange mailbox. A few things missing and non-intuitive and the English grammar of the messages is ambiguous (translated from Italian loses the warning messages' precision, it seems).
The biggest annoying thing about it is that when restoring from mbox files, even if you have exported the directory structure, the process flattens the structure, so all directories are in the root. The only way I found to prevent this was to not scan sub-directories when importing, and manually importing each directory which has sub-directories. This would be the biggest thing to fix (or make it obvious how to do this, if it is possible already).
The other thing is the export process. A warning is given for an IMAP mailbox: "You're exporting the local copy of a IMAP or NEWS folder. The local folder could not have all the messages present in remote folder. Do you want to continue?" .... so, does this mean that the export "does not" have all the messages or "might not" have all the messages?
If the plugin could advise on the process on ensuring that messages are included (sync and storage settings, perhaps?) or do this automatically for the user, that would be great.
Even just changing the wording in the warning and adding an explanation to the message would be useful!