Self-sealing envelopes that don’t! Luckily, I have a large bottle of rubber-type adhesive that does the job nicely.

It’s not only me that has the problem – I had a letter from my solicitor today (nothing sinister!) with the flap stuck down with Sellotape. Same post brought yet another letter with the same method of closure.
The one thing they had in common were the words ‘Seal-easy’ on each envelope.