It's possible to upload old messages from other email accounts to Gmail using your IMAP client, by transferring them to Gmail's web interface. If you'd like to upload messages, we have a few recommendations:
- Upload messages in small groups. Uploading is slow and can limit your available bandwidth.
- Messages that exceed Gmail's size limits will not upload.
- If you receive the error message 'Unable to append message to folder,' Gmail was unable to parse the message's formatting. Skip that message and continue uploading others.
Please note that uploading an excessive number of messages to Gmail via IMAP may lead to being temporarily locked out of Gmail. If this happens to you, please be aware that these lockouts are temporary and you should be able to re-access Gmail shortly.
While our engineers are working diligently to make the upload process faster and easier, we're currently unable to provide support for message uploading. We appreciate your patience while we work to improve Gmail.