What application produces a .lst file?

.LST files are generally application specific information text files and
definitely not a conventional extension for a contact information file.

First thing to do is open the file in a text editor to see if it in fact is
a text file with contact information in either a CSV or TAB delimited
format. If it is - rename the file with a .txt or .csv extension - and try
importing that file into Outlook - succes will depend on the quality of the
file format (ergo - if it doesn't work - it's not an Outlook problem).

Karl