01 / Locate the data you mean to protect.
In Thunderbird, use Help → Troubleshooting Information and the Profile Folder control to find the active profile. The application’s installation folder is not the mail profile. A profile can include mail, settings, address books and sensitive account data; treat its copy as private.
Our original example: Lena sees 2,400 messages in webmail, plus a desktop Local Folders archive labelled “2019 client work”. A working phone inbox proves nothing about that archive. Her backup inventory names both the server account and the local archive, rather than using “email” as one undifferentiated item.
Mozilla’s profile guide is the reference for locating, copying and recovering a profile. Close Thunderbird before a manual copy. Do not use a live cloud-synchronised profile folder as a substitute for an independent backup.
02 / Choose the copy route by size.
Thunderbird’s Tools → Export produces a ZIP archive, but Mozilla documents a 2 GB export limit. Use the official export instructions for a smaller profile; use the manual profile-copy route for a larger one. The planner below uses the conservative manual route at 2 GB or when size is unknown.
Example: a 0.8 GB IMAP profile may fit the export route, but you still inspect the output. A 6.4 GB profile with years of POP mail needs the manual route. Splitting an archive yourself or copying only a folder named “Mail” is not the same as preserving the complete profile.
03 / Verify something more than a filename.
Keep the original profile untouched. Record where the separate copy lives, when it was made and its approximate size. Check that the expected profile contents are present and that an archive opens without errors. A ZIP with an encouraging name but an unexpectedly tiny size deserves investigation.
A recovery rehearsal is a separate step. Use a separate profile or test environment and follow Mozilla’s recovery instructions; do not overwrite the only working profile to find out whether a backup is good. Before reconnecting a recovered mail client, understand that server actions can synchronise. If your aim is to preserve local history, inspect that history without making live account changes.
Keep “copy created”, “contents checked” and “recovery tested” as separate statuses. Our planner starts all three unchecked because filling in a form cannot perform any of them.