POST could be delivered later in Holmfirth as new rounds are introduced.
Royal Mail is bringing in new routes and delivery methods over the next few weeks.
The firm is writing to all households and businesses to explain what the changes will mean.
Royal Mail says that people are sending fewer letters because of e-mail while the number of parcels and packets have increased due to internet shopping.
That means the Royal Mail must “modernise” its service.
A company spokesman said Royal Mail would continue to deliver in the mornings in Holmfirth and for a longer period during the day. He said “many” customers would still receive mail by lunchtime.
The spokesman added: “The time customers receive mail will depend on where they live on the new delivery route.
“This may be later or possibly earlier than current delivery times. When mail volumes vary we may need to adjust delivery arrangements and times.”
The spokesman asked for the patience of customers while staff got used to the new system.
Royal Mail’s Heulyn Gwyn Davies said: “We are proud of the high regard in which our postmen and women are held in Holmfirth. The changes to delivery routes will mean that a member of our local and experienced team will still be delivering to our customers in Holmfirth.
“The local delivery team and I are fully committed to providing a high quality of service that is as reliable and friendly as customers have come to expect from Royal Mail in Holmfirth over many years.”
If customers have any queries after they have received a letter, they can call the Royal Mail’s Customer Services Team on 0845 601 1399.
Local councillors and business groups are also being advised of the changes.