In regards to NSF vs. PST size:
Generally in a mailbox folders are used to store information.
IN LOTUS NOTES
A folder contains only pointers (a pointer is an address of the message) to documents (mail messages).
It is possible in notes to copy (by dragging with the mouse and CTRL) a message into another folder but only a pointer is created in that folder not the whole message. Notes is efficient in that way.
A folder is outlook is like a directory in a file system, and a message is like a file. Each message in a folder contains the information not a pointer to the information.
If in Notes you have dragged messages to duplicate them in folders only the pointers and duplicated. The number of documents (mail Messages) in the database stays the same. In Outlook that get duplicated.
In Outlook if you copy or drag and hold CTRL a message to another folder you actually make a copy of the message. The PST will contain an extra message.
You can try this yourself in Notes by checking the database properties for the total documents. Then dragging a message and holding CTRL to another folder. The number of documents does not change.
When XitNotes exports it exports all information in all folders. If there are duplicates in one folder that are also in another it doesn’t check to see if that document was already exported (if it did people would wonder where the message went as they would expect it in that folder). Also if you have any non standard views in a database by default they get exported. You need to exclude them if you don't want them. Views can also contain duplicate data. For example the "All Documents" view which is excluded by default contains all the information and if exported would double the export size. If a user or administrator created a copy of the view and modifies it. It will be exported by default. You should exclude any NON standard views not wanted. You can do that in the INI file if you know the names. Otherwise export it manually using advanced.