Here's another way to access your User Library:

1. Double-click the Macintosh HD icon to open it.
2. Find the Users folder.
3. Open the Users folder.
4. Open the folder with your user name.
5. Open the Library folder (this is your User Library).
6. You should find a Preferences folder within Library. Open it and look for com.apple.mail.plist


Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365