Open-source alternatives to Microsoft Exchange

The cost is the sum of several components, and only some of them are software. Self-hosted OX App Suite with Dovecot, or openDesk, is free to download under its own licensing terms, so the main costs are infrastructure, the people who build and run the platform, and any paid support subscription you choose. Infrastructure recurs every month. Implementation, data migration and client rollout are one-time costs. Costs rise with mailbox count, data volume, the number of high-availability sites, and the number of integrations with directory, archiving, mobile and compliance tools. Ask any provider for a fixed-scope written quote that lists each deliverable, the environment it runs in, who operates it after handover, and which items recur each year. Confirm the licensing terms and any support tiers directly with the vendor before you compare totals.

The timeline depends on how much of the environment you need to move and how much you need to change along the way. No supplied source gives a duration for this kind of project, so treat any number a vendor quotes as a claim to verify. The main drivers are the number of mailboxes and total mailbox size, whether calendars, shared mailboxes, public folders and distribution lists must keep working, how many clients (desktop Outlook, mobile, shared devices) must be reconfigured, and whether directory integration and single sign-on need to be rebuilt. Migration waves, a pilot group and a rollback plan add time but reduce risk. Ask for a timeline by phase in the written scope, with explicit assumptions about data volume and user counts.

A migration needs decisions and access from your side as much as technical work. Expect to supply named owners for identity, mail flow, DNS and certificates, security and compliance, and the business owners who approve cutover windows. The team also needs read access to the current Exchange environment, a test tenant or staging environment, and a list of mailboxes, shared resources, retention rules and external integrations such as scanners, line-of-business applications and archiving tools. Users will need communication and some training. Confirm in the written scope who performs each task, because gaps in ownership are a common reason migrations stall.

A capable internal team can do it, provided it has people with hands-on experience in mail routing, directory services, certificates, backup and restore, and the chosen open-source platform. The harder parts are rarely the software installation. They are mail flow testing against external domains, anti-spam and anti-malware configuration, high availability, backup and recovery testing, and the coordinated cutover. Ask yourself whether those skills exist on the team now, whether anyone can take on operations after go-live, and whether the migration competes with existing projects for the same people. If the answer to any of these is no, a fixed-scope engagement covering implementation, hardening, backup and documentation may be a better use of budget than trying to learn under deadline. DeployOpen plans, implements, hardens, backs up and documents self-hosted platforms inside your own infrastructure, and provides ongoing support as a retainer.

PST exports are the common way to move mailbox content, but they are a poor format for ongoing use. Microsoft Purview eDiscovery can export Exchange mailbox items as PST or .msg files, and the export package expires 14 days after it is created. Exporting through this route requires a Microsoft 365 E3 or E5 license, so confirm your entitlement before you plan around it. Your plan should decide which content must be preserved, how legal holds and retention labels are handled, how PST files are verified and imported, and where they are stored securely afterward. Ask your legal and records teams to confirm the retention requirements in writing before any export starts, because the exit plan changes depending on whether you must keep an immutable copy of the source data.

Outlook can continue to be used with some open-source platforms, but the connection method, supported protocols and feature parity must be confirmed for each product before you commit. Users typically need new account profiles, updated server settings and, in some cases, a different client for calendars or shared folders. Some Outlook features tied to Exchange, such as certain delegate, rules, or add-in behaviors, may not work the same way. Test with a representative user group, including mobile devices and shared mailboxes, and document any changes users must make. Ask the vendor or implementation partner to list supported clients and known gaps in the written scope.

A useful quote lists scope, deliverables and timeline in writing before work starts. It should name the target platform and version, the environments covered, the number of mailboxes and data volume assumed, and the migration waves. It should also state what is included in testing, security hardening, backup and restore validation, documentation, user training and cutover support. Ask which items are one-time and which recur, such as support, upgrades and continuous testing, and what triggers a change order. Make sure the quote states who handles PST and eDiscovery exports, how exports are verified, and who is responsible for the final decommissioning of Exchange. DeployOpen does not publish a price list, and a quote follows from the written scope.