How do the messages appear in Print Preview? Have you got the scaling set to 100%?

Does Thunderbird appear to be using only a corner of the paper? Sometimes there is a glitch with your paper size which may cause the text to appear tiny because it is scaled down to fit in a small area. This thread has a suggestion for that scenario: https://support.mozilla.org/questions/1130744

Using full size of A4 paper. Just tiny print.

sounds like you correspondent may have specified a font size in their email. Folk using Microsoft mail clients routinely do this and it causes pain to everyone else.

Its not just one correspondent. it happens with all printed emails now wherever the source. the problem seems to be with me but I've no idea why. (Neither has my pretty techsavvy husband)

If you use 'Print Preview' what does it look like? If the font looks small, increase the 'Scale' value until it looks correct, then use 'Print'. Report back on results.

well lets look at it a bit at a time.

Print preview the email. Does it fill the page. is it readable?

What does the scaling say on the toolbar?

You appear to be using Windows 10. What happens if you choose to print to the built in PDF printer? Is it the same result?

Problem solved. thanks for trying to help. was resolved by amanchesterman wising me up to my % size. Doooooh. Thanks xx

Thankyou manchesterman. It was your response that saved the day xx

I had this problem too....when I looked at print preview, it was similarly very small, but when I changed the scale to 100%, it resolved the problem!