Post Office Savings Bank. 
POST OFFICE SAVINGS BANK
In James Mackay’s 1983 book Official Mail of the British Isles, he notes that the Post Office started the savings bank since “… the Post Office alone had the nationwide operation and expertise to carry it through.” While banks had been around for centuries, they were only for those who had plenty of money. By opening a savings institution for the small merchant or farmer, it helped them to succeed, and to add to the economy. The Post Office Savings Bank (POSB) was started in 1861 and allowed accounts for individuals and businesses.It must be remembered that this was the period where the concepts of time and money were becoming understood. No more burying the gold in the back yard or in one’s mattress. The POSB accounts required a minimum of 1 shilling to open with a maximum of £150 (later changed).
Ireland was covered by the POSB, and fairly large amounts were accumulated. Deposits were made through local post offices, and interest was posted to passbooks mailed in. The POSB somewhat delayed the separation of the Irish Post Office since it was necessary to wait until the end of the quarter to make a clean break. Even after 1 April 1922, passbooks were still sent to West Kensington (London) England since that is where the POSB was located. Of course, the British were reluctant to loose control of the Irish money, and it was some time before the Irish POSB functioned independently.
The Irish POSB is reflected in the mail stream. When passbooks were turned in for posting interest, they were returne to the owner by official mail. These are identifiable by the small rubber stamped DC, which stood originally for Dublin Castle, the one-time home of the POSB, Even long after the POSB moved out, the use of DC stamp was indicative of POSB mail. Mackay show five different designs (Figures 1 & 2) used along with two marked P Ch B (Post Cuntasior Baile Atha Cliath) (Accounting Dublin Postal District) (Figure 3).
To publicize the POSB, a special cancel was used on general mail advising the public of the opportunity (Figure 4).
To aid the public in finding the correct address, Economy labels were created so all the account holder had to do was stick them on the envelope. (Figures 5-7).
An example of a completed transaction is seen in figures 8-10. The payer has deposited £25.00 in his account, and receives a letter in the mail with a DC in a rounded square on the front (Figure 8). A copy of his receipt is seen in figures 9 and 10.
This is a mutually winning transaction for the payer and the government. The depositor could conveniently deposit from his home or office to accumulate a nest egg in an interest-bearing account, while the government has the use of the money needed for projects.