SIR,--Before taking up too much of your time, it is but fair to state that I shall not conform to the usage of society nor to the regulations of the Post Office. My communication will be anonymous, and, as you perceive, in the handwriting of a female. The dangers which beset the "usual channel," have forced me to take this course in offering an observation or two on the opposition to the extension of Sunday duty. This opposition in the office is not really against the duty, but is a strong attempt to level the author of Penny Postage, and was originated in Mr. ----'s room! The Clerks received the cue, and artfully led the Subsorters, Letter-carriers, and Messengers to believe that the duty was to be performed without pay. The Inspector of Letter-carriers lent assistance by expressing a determination to resign if the order came into operation. Old tales of cutting down of salaries on railway lines were revived, and anecdotes manufactured telling of meanness in private matters. The men saw what was expected from them, and were soon employed on their walks in announcing their doleful prospects and looking up mawworms to protest against such a prophane decree. Of the success of this plan out of doors, Sir, you are aware. In the office, the pretensions to piety are quite sickening. Fellows who have broken nearly every commandment are now fearful of causing ever so slight a flaw on the fourth. Still, there are plenty of men willing and able to carry out your object if certain of protection. That this is wanted, the following instance will show. The first man who made application for the Sunday duty was told it must be in writing. Before, however, he could put the few words required to paper, it was known all over the office. A system of annoyance was commenced, strong enough to deter him from proceeding further in the matter. He was hooted at inside the building and insulted in the street. Last night a report was in circulation that the morning despatch had been abandoned from the difficulty of obtaining hands. I hope, Sir, that this will not be the case with the evening duty, but that you will persist in the determination to benefit the public, in spite of in door opposition and out-of-door twaddle. Never mind if every letter is not got off on the first attempt--it will soon improve. Give the clerks an intimation that if they refuse this modification, it will be offered to the Subsorters on the same terms. They are afraid of us now. Educated in a better school--the Newspaper Office--for becoming officially dexterous, we could beat them at their own duties, and not one of them could accept a challenge to play the return match at those which we perform.