An Post could suffer from a hard Brexit because 60% of international parcels coming into Ireland come from the UK, according to the company's Chief Executive Officer.
Addressing the Communication Workers Union conference in Killarney, David McRedmond said the 30% growth of its parcels business from online commerce had offset the decline in traditional mail due to email, and had helped to convert last year's loss of €12m to an €8m profit.
However, he warned if the UK left the customs union, and customs checks were introduced, that would make things "extremely difficult and challenging".
He said that while it would be preferable for the current situation to remain unchanged, An Post would work to find solutions - including the possibility of basing warehouses of goods here in Ireland for distribution.
He noted that with 300,000 additional homes due to get broadband, it would mean increased parcel business due to more online purchases.
He also predicted potential growth in media mail - particularly after the General Data Protection Regulation is introduced.
Asked about the possibility of further restructuring or job losses, Mr McRedmond acknowledged that there would be more job cuts and changes, including staff moving from declining mail services to the expanding parcels operation.
However he stressed that the recent growth in profits had meant the scale of cutbacks would be less than it might have been.
He also pointed to the importance of growing financial services - especially Government business - through the post office network.
He said they were doing extremely well in building up financial services but were still "only in the foothills".
He cited the rollout of foreign exchange to all post offices, not just the larger ones.