Some interesting replies, Bravo for those
giving it a go. You are winners already by
taking the risk.
Stampgal would surely define the upper limit

I can see some educated reflection
in amongst the replies as well.
My Reference is the French Newspaper "L'Echangiste Universal"
I am only seeking "postage stamps"
but they give totals for....
Postage stamps
Service
Postage due
parcel post
franchise
express letter
newspaper
fiscal postal
and telegraph..
Of course the figure would be subject to debate,
but we shall use it at least as a basis for this comp.
Googlers..there is adverse karma for sneaking any peeps.
My guess would have been based on a middling country's
emmissions and multiplied by roughly the countrys
producing stamps, plus a few airmails for the new fledgling
service from remote locations.
Interesting to say the least.. you will be surprised.