If you print to a normal sheet of paper, does the address get printed, and
more importantly, whereabouts on the paper is it.  It may not correspond to
the position in which it should be when an envelope is loaded into the
printer and you may need to make appropriate adjustments.

For some ideas, see the "Correct Epson Envelope Orientation Problems" item
on fellow MVP Graham Mayor's website at:

http://www.gmayor.com/epson_envelope_orientation.htm