Exporting redirects
There are two places to export from, and they produce different files depending on what you need: editing and re-importing into one domain, or a full backup across everything.
Two places to export from
A specific domain's page exports only that domain's rules. The /redirects page, where you can view and manage rules across all your domains, exports everything at once. Which one you want depends on what you're doing with the file afterward.
Exporting a single domain
From a domain's page, exporting gives you a CSV with exactly the same four columns used for import: source_path, destination_url, redirect_type, notes. Because the format matches exactly, this file can be edited and re-imported straight back into that same domain, useful for bulk edits you'd rather make in a spreadsheet than one rule at a time.
Exporting everything at once
From /redirects, exporting includes every rule across every domain in your account, with an added domain column so you can tell which rule belongs to which domain. This format is for backup and reference, since it doesn't match the import format, a file exported from here can't be re-imported directly.
File naming
Domain-scoped exports are named domain-name-redirects.csv, so it's clear at a glance which domain a file belongs to.
Round-tripping through CSV
The domain-scoped export and import formats are designed to match. Export a domain's rules, make bulk edits in a spreadsheet, then re-import the same file to apply your changes, including resolving any conflicts row by row. See Bulk Import via CSV for how that import step works.
Related
For the full column reference, see CSV Import Format.