Royal Mail has removed "Humberside" from its address lists following a campaign by an East Yorkshire MP, 18 years after the county was abolished.
Humberside was set up in 1974 but replaced with four councils in 1996.
Graham Stuart, MP for Beverley and Holderness, said residents had been "irritated and exasperated" by the use of the defunct term on mail.
His campaign included stickers saying: "I don't live in Humberside, It's East Yorkshire. Return to sender".
The county of Humberside covered the north and south of the Humber Estuary from 1974.
It was replaced 18 years ago by Hull City Council, East Riding of Yorkshire Council, North Lincolnshire Council and North East Lincolnshire Council.
Royal Mail confirmed the name had been removed from their address database after Mr Stuart had a meeting with chief executive Moya Greene.
A statement said the change could take "a little time to filter down through address lists" and there may still be instances in which addresses have North or South Humberside "due to organisations not updating their databases or preferring to continue to use the term".
Conservative MP Mr Stuart said hundreds of East Yorkshire residents had used his stickers, which were paid for by the local Conservative association.
"This is a victory for my constituents," he said.
"I was so determined to see the back of Royal Mail's use of Humberside for my constituents that I made it an election pledge to get rid of it."
Leader of East Riding of Yorkshire Council Stephen Parnaby said it was "great news for the identity of the East Riding", but that it was a shame the issue had taken nearly 20 years to resolve.
Royal Mail has previously pointed out that historical county names were only made available for customers to reference "if they wished", and not actually required for postal purposes.