Dimissory Letters (Epistola dimissoriae).
(1.) In the ancient Church it was customary for any one about to travel to take with him letters of credence from his own bishop, if he wished to communicate with a Church in another country. These letters were of different sorts, according to the occasions or quality of the persons who carried them. Epistolae commendatoriae were granted to persons of quality, or to persons whose reputation had been called in question, or to clergymen who had occasion to travel in foreign countries. Epistole communicatoriae signified that their bearers were in the peace and communion of the Church, and hence were called pacificae, and ecclesiastiae, and sometimes canonicae. Epistolae dimissoria, at a later period, were only given to the clergy when they were to remove from their own diocese and settle in another: they were to testify that they had the bishop's leave to depart. All these went under the name of formatae, because they were written in a peculiar form, with some particular marks, which distinguished them from counterfeits. They were granted by the bishop's sole prerogative.
(2.) In the Church of England, dimissory letters are such as are used when a candidate for holy orders has a title in one diocese and is to be ordained in another: in such a case, the proper diocesan sends his letters, directed to the ordaining bishop, giving leave that the bearer may be ordained by him. In the Protestant Episcopal Church, certificates, or testimonials answering to the Epistolae dimissoriae, are required of clergymen passing from one diocese to another (Canon 5 of 1844). Similar provisions exist in other Protestant denominations. — Bingham Orig. Ecclesiastes book 2, chapter 5; Hook, Church Dictionary (Am. ed.), s.v.