Top pick: Thunderbird. Switching saves about $100 USD a year.
$99.99 USDa year
$115 CAD
Every pick below has a free version.
2 alternatives
The editor’s first choice for most people switching.
Best for a free open-source mail client on any desktop
Free and funded by donations. Exchange calendar and contacts sync is still in progress as of Oct 2026, so Exchange-heavy teams may prefer the Outlook client.
Covers most of the same work, with trade-offs noted on each card.
Best for a polished Outlook-style client for home use
The free license covers 2 accounts for non-commercial use only. Paid Personal and Business licenses lift the limits. Free version: Free for 2 email accounts and personal use only, no commercial use. Paid Personal and Business licenses lift these limits.
Sponsor this page: $149 for 30 days. Sponsors appear above the ranking, labeled; the ranking itself is not for sale.
How each alternative covers what people use Microsoft Outlook for. Numbers link to editor notes.
| Feature | Thunderbird | eM Client |
|---|---|---|
| Accounts | ||
| Exchange and Microsoft 365 accounts | PartialNote 1Native Exchange email over EWS and Graph; calendar and contacts do not sync through Exchange yet | YesNote 2Exchange and Microsoft 365 accounts are supported |
| Core | ||
| Calendar, contacts and tasks in one app | YesNote 3Calendar, tasks and address book are built in | YesNote 4Calendar, tasks, notes and contacts are built in |
| Calendar | ||
| Meeting invites and free/busy scheduling | PartialNote 5Sends and answers invitations; free/busy depends on the calendar server | PartialNote 6Meeting invitations are supported; scheduling depth varies by account type |
| Compatibility | ||
| PST files and Outlook data migration | PartialNote 7Windows import reads mail from an installed Outlook; PST files cannot be opened directly | PartialNote 8Imports PST and OST data files on Windows; does not write PST |
| Productivity | ||
| Rules, search and folders | YesNote 9Message filters, quick filter and global search | YesNote 10Rules and search are built in |
| Extensibility | ||
| Add-ins and integrations | PartialNote 11Thunderbird add-ons are a separate ecosystem; Outlook add-ins do not run | NoNote 12No add-in store is documented |
| Parity score | 67% | 67% |
Not covered by any free alternative yet: Meeting invites and free/busy scheduling, PST files and Outlook data migration, Add-ins and integrations. See all feature gaps
Can each alternative open and save Microsoft Outlook files?
| Format | Thunderbird | eM Client |
|---|---|---|
| .pst | NoNote 1No direct PST import; Windows can import from an installed Outlook | Opens onlyNote 2Imports PST and OST data files; cannot write PSTPartial fidelity |
| .msg | NoNote 3MSG files do not open without an add-on | NoNote 4MSG import is not documented |
| .eml | Opens and savesFull fidelity | Opens and savesFull fidelity |
| .ics | Opens and savesNote 5Import and export of calendar events and tasksFull fidelity | Opens and savesNote 6Calendars and tasks import from ICS filesFull fidelity |
Switching saves about $100 USD / $115 CAD a year. Prices checked .
Based on Microsoft 365 Personal, annual plan. Price source.
Last verified . Ranking: tier first, then the published score.
Something wrong or out of date? Report outdated info.
Microsoft Outlook is a product of Microsoft, named here for comparison only. Platforms listed for Microsoft Outlook: Windows, macOS, Web, iOS, Android.