H(enry) E(llis) Harris was a Boston stamp dealer, who for many years ran the largest volume approval business in the U.S. It was Harris' company that supplied the stamps for the Capt. Tim Healy stamp albums. I suspect that the envelopes you mention contained approval selections with some background info about the stamps on the envelope. If you have a scanner, put a scan or two up and you'll be sure to get more comments. I think Harris memorabilia is attractive and desirable, although not valuable. Below is are two scans of a 1928 Harris Christmas greeting that the company used as a stuffer for a cover it prepared to commemorated the 25th anniversary of the Wright Bros flight on December 17th, 1903.
Don

