Non-Postal Franking. 
Ireland and Britain shared an unusual situation where agencies other than the Post Office had the privilege of franking mail with their own indicia. This is the result of a court decision in 1879 where the Revenue Commissioners wanted to control their own mailings. A decision was made in favor of Revenue. A similar case was concluded with the Board of Trade being permitted to control their own operation. In Ireland this meant that documents, such as the “Application For A Certificate of Discharge From ‘Death Duties’”, also known as Form No.149, (Figures 1 and 2), were franked by Revenue rather than the Post Office. A similar situation existed with the Board of Trade envelopes. (Figure 3).
In Ireland, this situation was further exacerbated by the lack of legislation to require governmental agencies to reimburse the Post Office for delivering official mail. The rationale was that the Post Office budget included adequate funding to cover such mail. There were repeated attempts to require agencies to reimburse the Post Office, but none passed.
In 1946, the Irish Land Commission attempted to enter the fray. The Land Commission was one agency that used a significant percentage of the official mail. A logo was created, but the courts now sided with the Post Office. An example of the proposed logo is shown in Figure 4.
The entire question became a moot point in 1983 when the Ministry of Post and Telegraph was abolished and replaced by a government-controlled corporation known as An Post, thus ending official mail. Now all government agencies pay An Post for sending their documents by using stamps, meters, and/or permits.
Mackay, J., Official Mail of the British Isles, self-published, 1982.Chapters II & V