A second strike by postal workers was said to be "solidly supported" today, with some staff not involved in the walk-out refusing to cross picket lines.
The Communication Workers Union said picket lines were mounted outside mail offices across the country, adding that strikers were receiving "strong support" from members of the public as well as other unions.
Officials said an opinion poll showing that twice as many people sympathised with the postal workers than with Royal Mail management demonstrated the level of support for the union's case.
Half of the 840 adults questioned by BBC2's Newsnight sympathised with the postal workers and the union as opposed to the Royal Mail management (25%) and most did not want the company privatised.
The CWU has served notice of further walk-outs starting next Thursday to follow from today's walk-out by up to 78,000 delivery and collection workers.
A strike yesterday by more than 40,000 mail centre staff and drivers was also said to be solidly supported.
The union said workers not called out today, including drivers, refused to cross picket lines in areas including parts of Yorkshire.
Jim McKechnie, branch secretary of the union's Glasgow and district branch, said around 4,000 of the area's workers were involved in today's action.
Following a visit to delivery centres in and around the city, Mr McKechnie said: "A lot of people are unhappy with the way things are going.
"We've just got to keep morale up and hopefully we can avoid next week's strikes.
"We need a resolution and the public can start getting their mail delivered. Our door is open for talks. This cannot be sustained."
Mr McKechnie said mail centre staff planned to walk out from 4am next Thursday, while delivery workers are scheduled to strike from 9pm next Friday.
The union has offered "unconditional" talks at the conciliation service Acas in an attempt to break the deadlocked row over jobs, pay and modernisation.
Royal Mail managing director Mark Higson said it was "appalling but sadly not surprising" that more strikes have been called.
The new stoppages will cause further disruption to mail deliveries, which are already facing big delays because of this week's action.
Prime Minister Gordon Brown urged Royal Mail management and postal workers to get "round the table" to solve the dispute, saying the strike was "self-defeating".Reuse content