Official Mail. 
Official Mail refers to mail emanating from government departments on official government business. Most departments have their own pre-printed envelopes, postcards or forms. The varietydifferent departments and stylesenvelopes is quite staggering. More recently many offices used a generic envelope to which they would apply their department cachet and/or an adhesive address label.
On Her Majesty’s Service 1837-1901
Inland Revenue cover from Dublin to Dalkey with 6 Jan.1887 OFFICIAL PAID handstamp.
As one can imagine, the Inland Revenue produced many covers and these are quite common especially in the later halfthe 20th century.
On His Majesty’s Service 1901-1922
Uncancelled Post Office form letter dated 3 July 1925, still using pre-independance stationery for departmental correspondence. No postal markings.
The transferauthority and controlthe Post Office to the Irish Free State government took place on April 1, 1922.
The printing warrant inside this form indicates it was printed in March 1920.
Irish Free State 1922-1937
InspectorTaxes registered envelope used from Dublin to Blackrock (Co. Dublin).
‘BUY IRISH GOODS’ promotional meter slogan dated ’27 Oct 1926′.
Generic Saorstát Éireann envelope used with ÉIRE economy address label affixed and
franked with a 2 1/2d stamp because it is no on official business but for private use from Kanturk ’13 Jan 45′.
It seems the different Irish administrations did use up old stationery by either overprinting, especially between
1922-1925 or as in this case by providing a new label for old stationery.
Small generic RepublicIreland envelope as indicated by the ‘Harp’ design that was also impressed on the backsome envelopes instead.
The applicationa rubber certifying handstamps, in this case PresidentIreland, to generic envelopes became quite a common usage and there are many to collect.
Dated 26 Nov 1979.
Ireland’s Transition 1922-1925: Dr. Cyril I. Dulin, pub: MacDonnell Whyte Ltd, Dublin, 1992
Official Mail of the British Isles: James A. Mackay, pub: James A. Mackay, Scotland, 1983
Slogans on Irish Official & Paid Mail: F.E. Dixon, pub F.E. Dixon, Dublin, 1984
Irish Official Mail 1922-1983 Raymond Murphy, pub. Eire Philatelic Assn, 2018.