Any communication received without explicit consent, after providing details, is junk, and would fall under GDPR as using that info for a different purpose than what was described.

How is that different from a mail from a local church asking me to donate, or a local bingo club opening a new location - it's all junk. If I didn't ask for it to be sent to my address, it's all junk.

Pubs generate way more tax revenue than churches.

And I'm sure HSBC generate even more tax revenue, that doesn't mean that if they send me unsolicited mail about bank accounts it isn't junk.

One person's junk is another person's fuel for heating.

Throughout the year a friend of mine would collect any junk mail, but mostly many copies of the free daily newspapers (Metro, Evening Standard, etc) that litter the trains/underground in the evenings, soak them with water than use a briquette maker to press the paper into blocks. Once dried they provide an ample supply of fuel to heat his home for the 6-10 months of the year (depending on how poorly your home is insulated) that heating is required in the UK.

He definitely didn't have a "No junk mail" sticker on his letterbox.