An Post's State Savings fund grew by €1.9 billion last year according to its latest annual report.
The fund, now worth €18 billion, accounts for more than 16% of all personal savings in the country.
The annual report also documented an operating loss of €11.4m before exceptional items.
An exceptional credit of €17.1m, which relates to its pension scheme and a provision for future voluntary redundancies, resulted in an overall operating profit of €5.7m.
Profit after tax was reported as €5.9m.
An Post recorded a 22% growth in contract parcels and packet volume, which was predominantly driven by online shopping.
Traditional mail volume fell 2%, compared with 5% the year previous.
The group noted the quality of service performances for both inbound and outbound international mail exceeded targets, at 94.7% and 89.5% respectively.
It also noted that an agreement with staff to address the pension scheme’s fund deficit concluded last year.
An Post also secured a contract with the Department of Social Protection (DSP) for the provision of cash payments to DSP clients across the country.
An Post Chairman Christoph Mueller said it was critical to create a long-term financial model for a sustainable national postal service.