When writing an email all looks OK but after I've sent it when I look in my sent file I notice that the text size varies. The first paragraph is normally as I would expect it but often the second or third paragraph has a smaller text size. I'm definitely not changing anything and all the text is the same size before I send. The format boxes show Paragraph and Verdana, text size medium. In options the default font is Verdana 17. My operating system is Windows 10.

I have used Thunderbird for some years and not had this problem before. I've just changed computer and checked the settings on my old Windows 7 computer and ensured they are the same for my new one.