What language version of Thunderbird are you using? en-US or en-GB ?

When you go to File > Page Setup > Margins & Header/Footer tab At the top does it say 'Margins (millimeters)' or 'Margins (inches)' ?

I'm using English (British) downloaded from here:

• https://www.mozilla.org/en-US/thunderbird/all.html

English (British) is auto setup to use millimeters in File > Page Setup. it is also auto using A4 instead of Letter when printing.

The English (US) version is auto setup to use inches and Letter.

Options: Suggest you try to change the size type and then inches to millimeters

Tools > Options > Advanced > General tab or menu icon > Options > Options > Advanced > General tab click on 'Config Editor' button it will tell you to be careful :)

In top search type: size look for this line: print.printer_namexx.print_paper_size_type; Value = 0 (where printer_namexx = your printer name)

Value 0 = A4 Value 1 = Letter

look for this line: print.printer_namexx.print_paper_size_unit; Value = 1 Value 0 = inches Value 1 = millimeters

You can change any setting. right click on line and select 'modify' a small window opens, make the changes and click on Ok

then close the Config editor - top right X click on OK to close and save changes to Options.

Remember that the printer can also change the printing, so make sure it is set up for A4.

Thank you for the answer. Unfortunately all settings for paper size and unit in the configuration editor are okay.

And I have the dutch version, so everything is in millimeters etc.

What I noticed is that when I click the 'reset default values' in the properties tab of the printer (not sure what the exact name of the button is in the english version), it fills in the correct papersize A4 and the print comes out okay. But after printing and wanting to print a new mail, the 'letter' value is back again. So for some reason, it looses the default value.

I have another printer attached to my computer and for this printer letter is also used instead of A4.