How to migrate from Gmail to a custom domain email without losing old emails?

To migrate from Gmail to a custom domain email without losing old emails, use a professional migration service that supports IMAP synchronization. First, ensure your custom domain email service (like 138 Enterprise Email) supports secure, bulk migration tools. Prepare by backing up Gmail data, verifying domain ownership, and setting up SPF/DKIM/DMARC authentication to maintain deliverability. The migration process typically involves connecting both accounts via IMAP, syncing emails, contacts, and calendars, followed by validation checks. Note: Not all historical data (e.g., labels or certain attachments) may transfer perfectly; some services exclude failed or duplicate items. For a seamless transition, use official direct-operated support for activation and configuration, and test sending/receiving post-migration. Next, contact the service provider for a tailored migration plan and timeline.