A while ago I needed something to convert a 5GB Outlook OST file to PST format. Turned out Aspose has a good (commercial) API/library for Java to do exactly that. I had not touched Java for 10 years but got things sorted within a few hours thanks to clear instructions and good examples and docs. I just used the example and made minimal changes, nothing more.

Get files below or from Releases page

• Main executable: ost2pst.jar verify: SHA512SUMS
• Windows batch file: ost2pst.bat
• Linux/BSD shell script: ost2pst.sh
• If needed download Java here: JRE8 or alternatively: JavaSE-RE-8

Windows: ost2pst.bat <input.ost> <output.pst> (same for .sh)

• you can also run the jar directly: java -jar ost2pst.jar
• the jar needs JRE8
• Saving to Outlook 2013/2016 PST files is not supported

C:\src\ost2pst>ost2pst.bat input.ost output.pst

OST2PST (200316)

INFO: Loading OST file "input.pst" (5GB)
      Folder [00] "Public"
      Folder [01] "Inbox"
      Folder [02] "Outbox"
      Folder [03] "Sent Items"

INFO: File format is "64-bit Unicode" (23)
INFO: Converting "input.pst" to "output.ost" 511MB/4751MB (11%) |

• show file format info
• exits instead of trying to save outlook 2013+ files
• jar also builds in maven now

• error handling, added notice about outlook '13/16 files
• updated aspose-email lib to 20.2

• fixed (visual) error before convertion
• improved messages and progress indicator
• updated aspose-email lib to 19.12

• improved progress indicator
• updated aspose-email lib to 18.8

• pom.xml
• Loast2pstLoadAndConvertOSTFileCLI.java

• GitHub Aspose Email-for-Java
• docs.aspose.com Installation (Maven)
• docs.aspose.com Aspose.Email java for Eclipse (Maven)

• use Ant to 'Export', 'Java', 'Runnable JAR file' (used for ost2pst.jar)
• or alternatively use Maven to build project

Aspose.Email for Java: https://products.aspose.com/email/java
What lead me to Aspose: http://wiki.opf-labs.org/pages/viewpage.action?pageId=25887031
Possible alternative https://github.com/rjohnsondev/java-libpst

moved from old repo mkorthof/Aspose.Email-for-Java