For 50Gb I would use a dedicated zip program, Thunderbird export tools appear to tap out long before you get to something like that. That is a LOT of mail. Microsoft offer the following instructions [https://support.microsoft.com/en-us/windows/zip-and-unzip-files-8d28fa72-f2f9-712f-67df-f80cf89fd4e5 here ] <blockquote>Locate the file or folder that you want to zip. Press and hold (or right-click) the file or folder, select (or point to) Send to, and then select Compressed (zipped) folder. A new zipped folder with the same name is created in the same location. To rename it, press and hold (or right-click) the folder, select Rename, and then type the new name. </blockquote> This link contains information on how to locate your profile folder if you need it. https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-thunderbird-profiles