It depends on what you mean by "certain field".
What user action will select the field to be used?
Will each such address be in the same field of a different record (or this can be a set of fields for name, street, city, etc.)? That's the best approach here.
It may be simply a matter of setting up an envelope layout for printing, then you find or select the record you want before printing it on this layout with the Current Record print option to limit the output to just the current record.
Create a layout for printing the envelopes. Make sure you determine which table on which to base the layout. Then print a found set. A simple example is my year-end. I send out T4A forms to everyone I've employed in a given year. Why not have FM print the envelopes? I have a table called T4As. The envelope layout can be based on the same table. A script can find all records for a given year. Then the envelope layout will exactly mirror the Tax Form layout . . . Even the sort state. Of course the table could represent anything you like. My point is that an envelope layout can easily be based on an already existing table since one envelope will generally contain a printout of one record. RW