Unfranked Mail TO the Irish Government. 
While Official Mail FROM the Irish government to its people is well known, and traveled without stamps until the conversion of the Post Office in 1984. Less well-known is mail from citizens TO the Irish government that also traveled without stamps.(Figure -1) The authority for this was covered in Eolai an Phoist, in the 1982 edition on page 26. “… [letters] provided they are upon the business of the State, and addressed to a Minister or other high officer of the Government at his office, they are delivered without prepayment and without surcharge.”.
This mail is normally seen addressed to the Irish Land Commission from small towns since this is where the Land Commission did their work in breaking up large absentee-landlord estates, and returning the land to the descendants of those who’s land was seized. This program started in the 1870’s and reached a peak in the 1920’s. Other ministeries, such as Fisheries, Revenue, and Industry are known.
Besides the absence of stamps, the letter had to be addressed to an officer of the Agency, and bear the name, or at least the initials of the government. R.S.N.E. is short for Rialtas Sealdac na h’Eireann (Figure -2); SE for Saorstat Eireann.(Figure -3) One must guess that O.S.I.S stands for Official Service Irish State, but in any case, it went through the mails.(Figure -4). Eire is readily identifiable (Figure 5).
Is this official? Yes. Is it collectable? Yes. Is it pretty? That is in the eye of the beholder.
Eolai an Phoist, Volume 1, 1982.