Little confused about your process so to summarize to make sure I'm
understanding this:

#1 - Export your data to Excel from the DB (which database? - Outlook
supports Access directly just as a FYI)
#2 - Save the Excel worksheet as a tab delim text file (any reason you're
using Tab Delim instead of CSV?)
#3 - Importing the text file created in step#2 into Outlook (why not
directly import from the worksheet?)

Questions:
#1 - Are you sure that there are no extraneous "tabs" in any of your fields
causing the resulting rows to be incorrectly structured?
#2 - Are you explicitly mapping the email field when you're importing the
data?

Suggestion:

If you can't import directly from the DB file, and you don't want to import
from the Excel file, save the Excel data as a CSV file and import that file
explicitly mapping each of the fields. If you're just importing standard
fields and there are no issues with the raw data, Outlook's import wizard
works exactly as advertised.

Karl