MBOX vs PST: what changes during conversion

Which format works with Outlook?

An MBOX file is commonly used to store or export email from programs such as Thunderbird and Apple Mail. A PST is a data file that classic Outlook can open directly. PST can also hold Outlook contacts and calendar items, but an email conversion cannot create contacts or calendars that were not in the MBOX source.

Swipe or scroll to compare all columns.

Question	MBOX	PST
What it is used for	Storing or exporting mail in many email programs	Storing mail and other Outlook items
How messages are stored	Usually one mailbox file containing messages one after another	A structured Outlook data file with its own folders and indexes
How folders are stored	Often one MBOX file per folder, sometimes with companion folders created by the source program	Inside the PST folder tree
Can classic Outlook open it directly?	No	Yes
How to check it	Compare the files and folder list with the source mail program	Open it in Outlook and compare folders, messages, and attachments

MBOX has several variations, and each mail program may store subfolders or extra message details differently. If possible, keep a note of the program and version that created the archive. That information can help explain a missing folder or other conversion problem.

Why renaming the extension does not work

A filename extension tells a program which kind of file to expect. Renaming .mbox to .pst changes only the name, while the contents remain MBOX data. A converter must read every source message, translate its details into Outlook properties, recreate the folders, and write a valid PST.

What conversion should preserve

After conversion, compare the information you will rely on:

the folder tree and folder names;
sender, recipients, subject, sent and received dates, and message text;
attachments and pictures shown inside messages;
Internet headers, which record technical delivery details, if you need them for investigation or recordkeeping;
read or unread status, taking account of the Mark converted messages as unread setting;
Gmail labels, which may become folders or Outlook categories because one Gmail message can have several labels.

The features page lists what the converter is designed to retain. A small test with your own archive shows how its particular MBOX variation will be handled.

Size and performance planning

The PST will not necessarily have the same size as the MBOX source. Outlook adds folders, indexes, and other stored details, and a Gmail message with several labels may appear in more than one destination location. Attachments also have a large effect on size. Leave space for the source copy and the new PST files, and split a large conversion into smaller PSTs that remain comfortable to open and search in Outlook. Microsoft documents configurable PST limits and notes that performance can slow before the maximum is reached.

Which format should you keep

Keep the original MBOX unchanged until you have checked and backed up the PST. Use the PST as the copy you open in Outlook. For an important archive, also record the converter version, selected settings, date, source mail program, any error log, and your verification results. You can record a file hash—a calculated digital fingerprint—for both files if you need to prove later that neither one changed.

Primary sources

FAQ

Do all MBOX files work the same way?

They share a basic format, but mail apps can store folder information and message details differently. Keep the original folder structure and try a small mailbox before converting the full archive.

Can I convert MBOX by changing the extension?

No. MBOX and PST store email differently. You need to convert the contents, not rename the file.

Does MBOX include contacts and calendars?

No. MBOX stores email messages. If you also need contacts or calendar events in Outlook, export them separately from your original app or account.