Split PST File into Smaller Parts

📦 One Outlook data file has swallowed eight years of mail. Search crawls, the backup job times out, folders take a moment to open. Outlook offers no way to divide such a file, and an archiver only makes volumes that no mail program will mount. Split PST File does the job the way it has to be done: it reads the archive on your own PC and writes several smaller PST files, each one valid on its own.

❔ Why Outlook cannot split PST files itself

A .pst behaves as a single database, and a database has no seam that a file tool could pry open. Compact Now, the only size tool in the program, reclaims the space that deleted items left behind and nothing else, so a file genuinely full of mail barely moves. AutoArchive shifts items by age alone and hands back a second file that grows in turn. The older ANSI layout runs out near two gigabytes and turns fragile at that edge, while the Unicode layout reaches 50 GB by the MaxLargeFileSize registry value and grows sluggish long before that.

⚙️ Four rules to split PST files by

By Size stops every part at a ceiling you name, one gigabyte unless you say otherwise, and always cuts between messages, so a heavy letter becomes a part of its own rather than being torn across two files. By Date period groups mail by year, month or ISO week and names the results 2023.pst or 2024-01.pst, with undated items kept aside in a part of their own. By Folder sends every top-level folder out as its own file, hierarchy intact. By Sender routes correspondence per address and pools rare ones into others.pst, so a mailbox does not end as a thousand tiny files.

👍 What a Split PST File run leaves behind

• 1️⃣ What you load is read and never written to; the parts appear as brand-new PST files elsewhere.
• 2️⃣ Both .pst and .ost are read straight off the disk, with no Outlook installed or running.
• 3️⃣ A folder tree with checkboxes drops whole branches before the run even starts.
• 4️⃣ Deleted Items and Junk stay out of the parts while the box for them is ticked.
• 5️⃣ A CSV report names every part written, how many letters went in and what it weighs.
• 6️⃣ A repeated name takes a numbered suffix rather than overwriting what is there.
• 7️⃣ Every part mounts through File, Open and Export, Open Outlook Data File.

ℹ️ Free to try. Unregistered, Split PST File walks the whole tree and processes a sample of the mail, which is enough to watch a rule divide your own archive before anything is paid for.

❓ Who needs to split PST files

• ✅ Admins holding an inherited archive that no backup window can swallow whole.
• ✅ Legal and compliance work, where one custodian or one year has to leave on its own.
• ✅ Long-time Outlook users whose single file has become one point of failure.
• ✅ Anyone moving mail somewhere with an upload limit measured in gigabytes.

❓ Frequently asked questions

❔ Can I split PST files by year?
💡 Yes. Choose By Date period and set the span to year, and each calendar year leaves as its own file. Month and ISO week are there when finer archives are wanted.

❔ How do I reduce the size of a mailbox that is already too large?
💡 Compacting recovers only free space. Split PST File is the physical answer: the mail itself is divided, and each part opens on its own.

❔ What tool helps when Outlook will not even open the archive?
💡 This one reads the closed file from disk, so a mailbox that no longer loads can still be divided. PST and OST both work.

Questions, trouble or a missing feature: write to us, we answer.