The scheme is being rolled out to 3,300 boxes north of the Border which carry 50 items or less a day as they do not cover their costs.
Collection times have been cut by up to nine hours with the last daily pick-up at some boxes now 9am Monday to Friday when it was previously 6pm.
The changes mean that first class letters posted later than 9am are unlikely to be collected until the next day.
On Saturdays those times have been cut, in some areas, to 7am when customers previously had until 12 noon to post letters.
Royal Mail confirmed last week that 1,155 boxes have so far been identified as moving to the new arrangements. The rest will be rolled out over the next year.
The majority of boxes moving to collection on delivery are in Glasgow and Edinburgh.
SNP postal services spokesman Mike Weir said: “Consumers and businesses will be rightly furious.
“The Royal Mail sell-off has been a shambles since day one. The majority of Scots were opposed to the privatisation of Royal Mail.
“We need a service that meets the needs of our communities and one which is brought back into public ownership.”
A third of Scotland’s 10,000 postboxes are moving to collection on delivery and the process will take up to two years to complete. Royal Mail claim there will be no effect on the service to customers as boxes with later collection times are available within half a mile.
A spokesman from Royal Mail said: “A decline in letter volumes means many postboxes no longer cover costs.
“The collection from certain postboxes will be carried out by the local postman or woman on their route, at a time dependent on where the box is located.”
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