You may get a response if you explain what you mean by having a backup of your gmail account.

Sorry for not explaining fully enough. I have used gmail for years and have circa 10Gb of history which I need to keep. I want to transfer the oldest of my gmail history to an offline store, so Thunderbird was recommended as a way to access the data. I used google's 'Takeout' service to export the gmail data as a single file. This comes as a zipped mbox file.

Having extracted it, I tried to link the mbox file to Thunderbird using the ImportExportTools NG addon and selecting the Import Individual mbox file.

The original post above is the outcome.

I.e.

[Exception... "Component returned failure code: 0x80550005 [nsIMsgFolder.msgDatabase]" nsresult: "0x80550005 (<unknown>)" location: "JS frame :: resource://mboximport/content/mboximport/modules/mboxImportExport.mjs?14.1.7 :: rebuildSummary :: line 706" data: no]

rebuildSummary@resource://mboximport/content/mboximport/modules/mboxImportExport.mjs?14.1.7:706:5 _importMboxFile@resource://mboximport/content/mboximport/modules/mboxImportExport.mjs?14.1.7:415:16

I suggest you do this: - exit thunderbird - copy the mbox file after export to the Mail\Local Folders folder in the profile - start thunderbird

That is usually enough. all the addon does is that it does the copy while thunderbird is running.

Thanks to david for the suggestion. For others looking for a solution like my issue the folder David refers to - on my Windows 10 PC - is here. C:\Users\ian\AppData\Local\Packages\MozillaThunderbird.MZLA_h5892qc0xkpca\LocalCache\Roaming\Thunderbird\Profiles\wz8zi079.default-esr\Mail\Local Folders

It is NOT where Thunderbird suggests it is - if you right click a local folder and select Properties !!!

The location is at ...appdata\roaming\thunderbird\profiles\<profilename>\Mail\Local Folders if users install from the official site, thunderbird.net. If you install the Microsoft version, it does not work the same and some troubleshooting features are unavailable