The short answer
PST (Personal Storage Table) is a proprietary file format created and owned by Microsoft for use with Outlook. Apple Mail is built on entirely different, open-standard email formats — mbox and emlx. The two formats are architecturally incompatible, and Apple has no obligation or incentive to build a PST reader into Mail. If you have a PST file and want to read it in Apple Mail, a conversion step is required.
What PST files are and why they exist
Microsoft created the PST format to store all of a user's Outlook data — emails, folders, contacts, calendar entries, and tasks — in a single local file. PST stands for Personal Storage Table and was introduced in the 1990s as a way to archive Outlook data offline. The format is tightly coupled to how Outlook organises and indexes email, making it a natural fit for Outlook but difficult to implement in other clients.
What Apple Mail uses instead
Apple Mail stores email using two open formats:
- mbox — a widely supported open standard that stores multiple emails in a single plain-text file. Used for mailbox exports and imports across many email clients.
- emlx — Apple's own per-message format, derived from mbox, where each email is stored as an individual file. This is what Apple Mail uses internally on disk.
Neither format has anything in common with PST's binary structure.
PST vs Apple Mail formats at a glance
|
PST (Outlook) |
mbox / emlx (Apple Mail) |
| Created by |
Microsoft |
Open standard / Apple |
| Format type |
Proprietary binary |
Plain text / open |
| Used by |
Microsoft Outlook |
Apple Mail and many others |
| Natively readable by Apple Mail |
No |
Yes |
Why Apple hasn't added PST support
It is a competitor's proprietary format. PST was designed by and for Microsoft Outlook. Apple has no contractual or technical obligation to implement it, and supporting a competitor's closed format is rarely a priority.
Apple Mail is built on open standards. Apple's approach to email has always been to use open, interoperable formats. PST does not fit that model.
Low demand relative to effort. The majority of Apple Mail users have never touched a PST file. Adding a complex binary format parser for a niche migration scenario is a significant engineering effort for limited return.
What this means if you have a PST file on Mac
If you have a PST file — whether from a Windows PC, a former employer, or an Outlook for Mac export — Apple Mail cannot open it as-is. The practical solution is to convert the PST file into mbox format, which Apple Mail can import directly. This conversion can be done offline on your Mac without uploading your email data anywhere.
Frequently Asked Questions
Why doesn't Apple Mail support PST files?
PST is a proprietary Microsoft format. Apple Mail uses open standards — mbox and emlx — which are incompatible with PST. Apple has no obligation or incentive to implement a reader for Microsoft's closed format.
Will Apple ever add PST support to Apple Mail?
It is unlikely. Apple Mail has been built on open email standards for decades, and there is no indication Apple plans to add native PST support.
What format does Apple Mail use instead of PST?
Apple Mail stores email using mbox files (an open standard) and emlx files (Apple's per-message format). Both are fundamentally different from the PST format used by Microsoft Outlook.
How do I open PST files on a Mac if Apple Mail doesn't support them?
Use an offline PST to Apple Mail converter. It reads the PST archive directly on your Mac and produces output that Apple Mail can import via File > Import Mailboxes.
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