A new An Post report shows the company pays men almost 4% more than women.
The figure shows the difference in the hourly rate and is well below the national average of 13.9%.
It is part of the company's gender pay gap report which also shows the company has a 50/50 split of men and women on its board of management.
However, only 25% of its 9,000 workforce is made up of women.
An Post chief of staff Aoife Beirne says the company is on the right path but it still has work to do.
"What we saw is that by publicising this report, we are publicly committing to gender equality," said Ms Beirne.
It's worth noting that we are not perfect but we do have a good story to tell and we recognise that we want to be more inclusive workplace.
"So it is our commitment that both internally and externally that we will make that change happen."
Ms Beirne said that other companies should look at publishing.
"Once we got our data and could show that we had a gender pay gap of 3.7%, we were able to look into it then and see what is it that we need to do to be more inclusive."
She said that she would "fully recommend" that other companies got through the process.
