The (still growing) list of books in CEMROL containing English letters includes:

• The Earl of Arlington, Letters to Sir W. Temple, London, 1701 (also contains French and Latin letters).
• Robert Boyle and Gilbert Burnet, Some Letters […] Written by G. Burnet […] to […] Robert Boyle, [London], 1708 (3rd ed.).
• Richard Fanshaw et al, Original Letters of his Excellency Sir Richard Fanshaw […], together with Divers Letters and Answers from the Chief Ministers of State of England, Spain and Portugal, London, 1702.
• Alexander Pope et al., Letters of Mr. Pope and Several Eminent Persons, from the Year 1705, to 1711, vol. 1, London, 1735.
• Jonathan Swift, ed., Letters written by Sir W. Temple […] and Other Ministers of State […] from 1665 to 1672, 2 vols, London, 1700.