Is it proper for an attorney to send copies of letters written to opposing counsel to the opposing counsel's client?
Tex. Comm. On Professional Ethics, Op. 358, V. 35 Tex. B.J. 106 (1972)
Canon 9.
As a general rule, an attorney should not send copies of his letters that are written to opposing counsel to opposing counsel's client; however, an attorney may send to the opposing counsel and to the opposing party a demand that such party submit to a physical examination. See Canon 9; also Opinions 97, 101, 130, 139, 163, 170, and 355. (9-0.)
An attorney should not, as a general rule, send copies of his correspondence with opposing attorney to the opposing attorney's client.
Tex. Comm. On Professional Ethics, Op. 358 (1971)