Open an MBOX file — no mail client needed

Ask Google for your Gmail and you get MBOX: one plain-text file with every message concatenated, each introduced by a line starting with "From ". There is no folder tree inside it, because Gmail does not have folders. Labels survive as an X-Gmail-Labels header on each message, and threading survives as ordinary References and In-Reply-To headers. Mailward reads that label header and rebuilds your labels as browsable folders in the sidebar — a message carrying three labels appears under all three — so the structure Gmail's interface implied comes back, instead of one flat wall of messages.

The practical problem is size. A decade of mail is routinely several gigabytes in a single file, and the standard advice — install Thunderbird, create a profile, add ImportExportTools NG, import, wait — is a lot of ceremony when the actual goal is to find one message from 2019.

Mailward reads the MBOX directly in the browser without loading it whole. That matters more than it sounds: a browser tab cannot hold a string longer than about 512 MB, so any viewer that decodes the file as one piece of text fails outright on a large Takeout — that was the previous version of this page's reader. The current reader scans the file once in 4 MB chunks, records each message's byte range, and re-reads just that range when you open a message. Subject and sender search use the index and answer immediately; body search re-reads messages as it goes, so on a very large mailbox it takes longer and reports progress as it scans. The free tier reads the first 500 MB — what the old whole-file reader could ever open — and the whole mailbox is listed and searchable; reading past that mark is the Pro part.