Across personal mailboxes and business domains alike, Mail-Archiver captures, indexes, and preserves every incoming and outgoing email from multiple IMAP and Microsoft 365 accounts in a tamper-resistant archive. Connect standard IMAP servers, Microsoft 365 business tenants via Microsoft Graph, or personal Outlook and Hotmail accounts using OAuth2 device code flow without creating custom cloud app registrations. Scheduled background synchronization mirrors complete folder hierarchies automatically, while bulk tenant onboarding lets administrators import every active mailbox from a Microsoft 365 organization through a single configuration screen. When an important contract, invoice, or correspondence thread goes missing, the advanced search interface filters archived messages by sender, recipient, subject, date range, folder, and body text with instant HTML preview and direct attachment downloads. Users can import legacy MBox files or zipped EML archives, export selected messages or entire accounts, and run direct mailbox-to-mailbox migrations that copy folder trees between providers. Granular retention rules optionally purge aged messages from upstream mail servers to free quota while keeping local archive copies locked against manual deletion for compliance auditing. Multi-user access controls, OpenID Connect single sign-on, detailed activity audit logs, a scoped read-only REST API, and a Model Context Protocol endpoint allow both teams and AI assistants to query historical mail safely. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. GPL-3.0 licensed.