Move from an export file

Bring the history of a mailbox into Yuva from a file you exported, without giving Yuva any access to the account. This suits a very large mailbox, a program that has no IMAP, or an account Yuva cannot sign in to. The overview is in Move to Yuva.

Open Settings → Move to Yuva → New migration, enter the address the mail was sent to, open Or upload an export file, choose Google Takeout or Export file and pick the file. Then choose what to bring, scan and copy as in any other migration. The file is checked and read on the server; Yuva never changes it.

Files Yuva reads

File	Notes
Google Takeout .mbox	Unzip the Takeout archive first and upload the .mbox file from its Mail folder. Gmail’s labels and threads come with it.
An .mbox file	mboxrd (what most programs write) or, under “mbox options”, the older mboxo.
A .zip of .eml files	Its folders become labels.
A .zip of a Maildir	Its folders become labels.
A .zip of .mbox files	Each file becomes a label. The .mbox files must be stored uncompressed in the zip.

Yuva does not read .tgz or .gz files, compressed .mbox files inside a zip, or Outlook’s .pst files. Unzip an archive and upload the .mbox inside it.

Limits

Limit	Value
Size of one upload part	8 MiB
Size of one file	20 GiB, set by the server’s YUVA_MIGRATION_UPLOAD_MAX_BYTES
Entries in a zip	1,000,000
Compression of a zip entry	at most 100:1

Messages larger than YUVA_MIGRATION_MAX_MESSAGE_BYTES are skipped, as in every migration. One file per migration; for another file, start a new migration.

Upload and resume

The browser cuts the file into 8 MiB parts, sends several at once and retries a part that fails. Keep the page open. If the connection drops, the upload goes on when it is back. If the page was closed or reloaded, open the migration again and pick the same file again: Yuva compares what it already has and sends only the missing parts. A different file is not mixed in; the page asks before it sends that one from the start. When all parts have arrived, Yuva reads the file and tells you its format.

When the file is refused

Yuva checks a zip before it reads anything from it. A refused file’s uploaded parts are deleted; fix the file and upload it again.

Reason	What it means
unknown_format	It is neither an mbox nor a zip.
empty	There is no message in it.
corrupt	The zip cannot be read; it may be damaged or cut off. Make it again.
path_traversal	An entry has .. or an absolute path in its name.
symlink	An entry is a symbolic link. Make the zip again without links.
too_many_entries	The zip has more than 1,000,000 entries.
zip_bomb	An entry is compressed more than 100:1.
entry_too_large	An entry is larger than the server’s limit for one file.
encrypted	An entry has a password.
unsupported_compression	An entry is neither stored nor deflated.
compressed_mbox	An .mbox inside the zip is compressed. Unzip the archive and upload the .mbox itself.

A file larger than the server’s limit is refused before it is sent. If the server’s limit is 0, file imports are off.

The file is deleted

The uploaded parts, and so the file, are deleted when the migration completes, is cancelled or is deleted. Yuva keeps only what it imported. The migration page says when the file was deleted.

Get a file out of your mail

Each page below is the program’s own help.

• Google Takeout. Open Google Takeout, select only Mail, choose a one-time export as Zip files, and create it. Google emails you a link when the archive is ready, which can take from minutes to days; the link works for about 7 days and 5 downloads. Unzip the archive and upload the .mbox file from the Mail folder. Google’s page: Export your Google data.
• Apple Mail. Select the mailboxes and choose Mailbox > Export Mailbox. Mail writes each one as an .mbox file. Apple’s page: Import or export mailboxes in Mail.
• Thunderbird. Thunderbird keeps each mail folder as an mbox file in your profile. Mozilla’s page: Profiles - Where Thunderbird stores user data. Upload a folder’s file.
• Outlook. Outlook exports to .pst, which Yuva does not read. Convert the .pst to .mbox or .eml files with a conversion tool of your choice, put the .eml files in a .zip, and upload that. Microsoft’s page: Export or back up email to an Outlook .pst file.
• Proton Mail. Proton’s export tool writes .eml files. Put them in a .zip and upload it. Proton’s page: Export emails.

Very large Gmail mailboxes

Start with a Takeout file, then connect the mailbox over IMAP for the newer mail and the switch: see Gmail and Google Workspace.

From your backend

Owners, admins and API keys without an inbox limit that hold migrations:manage. Start a migration with a file or takeout preset, then:

Endpoint	Use
GET /v1/migrations/{migrationId}/upload	The parts the server has, to resume a cut upload.
POST /v1/migrations/{migrationId}/upload/parts/{part}	Send part part (from 0): a file of at most 8 MiB and its sha256, as multipart/form-data. Parts may arrive in any order and in parallel.
POST /v1/migrations/{migrationId}/upload/complete	Check the parts and read the file; the migration becomes connected.

Errors worth handling: 413 part_too_large, 422 checksum_mismatch (the part is not stored), 422 hosted_limit (the file is over the server’s limit), 422 upload_incomplete (missing_parts names the first missing parts), 422 file_refused (reason, and the zip entry when one is to blame) and 409 migration_state. The rest of the flow is in Move to Yuva; full shapes are in the API contract.