Younger readers may not even be able to imagine a time when paper was really the only common medium for writing and sending messages, but it wasn't that long ago. Even the new-fangled fax machines used paper. (I will steer clear of telegrams at this point, in case we have another Morse code outbreak like the other week!)
The Filofax range used to include specific inserts for the purpose. Around 1987 (when, admittedly, the sheer variety of specialist leaves offered was starting to get a bit silly) one could buy envelopes like these in white, pink, lavender, fawn, grey or blue!
They were slightly larger than the standard inserts of course, but would still fit nicely in the wallets.
For special occasions one could send a Filocard.
The designs were Punch magazine cartoons. This one was a dig at the 1980s trend associating a large and well stuffed Filofax with a successful career and busy social life.
Office life prior to the widespread adoption of networked PCs involved a lot of circulating paper. So rather than sending an email you would very probably use a memo.
I wonder if anyone out there remembers using any of these?