SFTP in PASE, updating access automatically

Daily, I send files manually to a vendor using a Windows client - FileZilla. 
Our system now has PASE and sftp.  And, I was able to send a file that way as
well.

The problem is that they change servers at somewhat random intervals.  FileZilla
manages to update whatever needs updating and things continue on nicely.

The technical person at the client end, seemingly familiar with sftp, does not
know how to coax sftp to behave in the same manner as FileZilla does.

Which brings up a bunch of questions, these for openers:

1) Is FileZilla performing some tasks without benefit of encryption?
2) How is FileZilla able to so easily deal with a change in the host?
3) Can sftp be configured to be tolerant of machine changes?
4) Should it even be considered?

I can likely think of more to add to the above.  Right now, this FileZilla thing
is kind of like a leash.  Somebody has to use a pc DAILY (thankfully, only
Monday-Friday) to transfer data.  The only method that the vendor will support
is sftp - which, compared to plain jane FTP, is not as predictable as far as
determining success/failure under program control.  By that, I mean that sftp
does not utilize numeric codes - at least not that I have seen as yet.  Thus,
determining "success" or "failure" does not appear to be simple - when done
with program code.


Any thoughts?

John McKee