What your recipients see depends partly on what you have in Tools/Options/Composition/General/HTML. Do you have Size set to Medium, the default? Even if you do, their settings may override this.

What you see when you receive mail depends on your settings in Tools/Options/Display/Formatting/Advanced. What do you have for the Size settings for 'Fonts for:' Latin and Other Writing Systems, and do you have 'Allow messages to use other fonts' checked?

Size is set to medium.

Fonts for Latin and use other fonts is checked.

This changed after the "update" to v60. So I haven't done anything to do this.

If you increase the Size settings in the Advanced options, for both Latin and Other Writing Systems, and uncheck 'Allow messages to use other fonts', do you see the font size change in your received messages?

It isn't my received messages, it is the people that receive my messages.

You can try changing the Size from Medium to Large and see if that satisfies recipients, without others complaining it's too large. It's probably futile to compensate for others' inability to manage their email programs.

Yeah, thanks, but see, that's not helping. This started, again, AFTER, the forced update to to v60.

Please don't respond as I don't want to waste any more of your time.

Dear, I had also this issues (font too small in some message) after updating to TB 60.x

After many search...I found the "cause". This append when the font size is not specified in the html code of a message (when you display the source code of the message). Trying to resolve this by changing option in the option, display/advance and compose settings did not help.

I found this solution to this issues : Go to tools, options, advance panel, config editor, and search about "font.size". Reset each specified value by the default value (right click reset).

Minimal font size was restored to a correct value (and for my eyes :D ). I hope it help...