Microsoft Outlook alternatives

Open-source alternatives

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  Thunderbird

  Fit: PartialCore overlap exists; named gaps need replacing or rebuilding.Fit is not feature parity. A Tier ANo paid feature gates in the self-run edition Mozilla Public License 2.0 Permissions of this weak copyleft license are conditioned on making available source code of licensed files and modifications of those files under the same license (or in certain cases, one of the GNU licenses). Copyright and license notices must be preserved. Contributors provide an express grant of patent rights. However, a larger work using the licensed work may be distributed under different terms and without source code for files added in the larger work. May Commercial useModificationDistributionPatent usePrivate use Must Disclose sourceLicense and copyright noticeSame license (file) No LiabilityTrademark useWarranty Summary from GitHub's choosealicense.com Self-hostable: noNot offered as software you run yourself.

  Local alternative for email, calendars, contacts, tasks, and multi-account organization. Reconnect mail accounts using supported authentication; Microsoft-hosted accounts may require OAuth, SMTP enablement, and administrator consent. Full Exchange/calendar or Microsoft 365 suite parity is not asserted. Existing subscription storage/security benefits are separate from the client.

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  Roundcube

  Fit: Different approachSolves the same job differently; plan a redesign, not a copy.Fit is not feature parity. A Tier ANo paid feature gates in the self-run edition GNU General Public License v3.0 Permissions of this strong copyleft license are conditioned on making available complete source code of licensed works and modifications, which include larger works using a licensed work, under the same license. Copyright and license notices must be preserved. Contributors provide an express grant of patent rights. May Commercial useModificationDistributionPatent usePrivate use Must License and copyright noticeState changesDisclose sourceSame license No LiabilityWarranty Summary from GitHub's choosealicense.com Self-hostable: yesYou can run it on your own server.

  Browser webmail alternative for ordinary mailbox access using your own compatible IMAP/SMTP service. Requires server deployment; contacts and messages have import/export tools. Core Roundcube is not a replacement for the Microsoft 365 suite, hosted mailbox service, or Exchange calendar workflows; calendars are third-party additions.