An Post has confirmed that 161 postmasters have applied for voluntary retirement.
It follows the announcement earlier this year of the company's post office transformation programme and a €50m investment in the post office network.
An Post said the retirements will likely result in the closure of 161 post offices out of a network of 1,111 offices.
The list of post offices closing will be issued at the end of this month once the details are confirmed with each postmaster.
The voluntary retirement package was agreed with the Irish Postmasters' Union (IPU).
In a statement, An Post said the company, the IPU and postmasters are in agreement that the consolidation of the network and the subsequent transfer of business to neighbouring offices is essential to the sustainability of the overall network and the continued provision of services in local communities.
Mail delivery and collection services are not affected by the closures.
An Post said it reaffirms its commitment that communities of over 500 people will have a post office and that over 95% of the population will be within 15km of at least one post office.
All island post offices are being retained.
An Post will also publish a target list of new post office locations at the end of this month.