1915 2e Regt Etranger Depot d’Orleans

On the 4th of May 1915 an unknown sender, wrote a letter from Orleans to:

Madame F Ziegler
5 rue Debelleyme
Paris III

what currently remains is the cover of this letter,
The sender dit not put his name on the cover, but in pen is written

2e Regt Etranger Depot d’Orleans * Service Postal *

In pencil:
2^m regt etranger
3^o Cie Beaumont

A purple colored stamp reads:

2e Regt Etranger
Depot d’Orleans
Service Postal