Commercially Used Covers and Postcards have actually passed thru the postal system. I find the authenticity much more interesting than covers posted by someone with one eye on a stamp album.
This first cover was sent from County Donegal to an Irish Language newspaper “Lá” in Belfast. Note that it is written in Gaeilge.
This second cover, I posted from Dundalk, County Louth. It contained a Valentine card for my wife.
We should never lose sight of the fact that the postal service is an amazing institution that we take for granted.