When Outlook Fails Twice: A Strange Case of Synchronized Corruption

Recently, I encountered a puzzling issue that I haven’t seen before—at least not with this kind of symmetry.

An end user reached out to report that Microsoft Outlook was freezing on both of his computers. Each time he clicked the icon, Outlook would launch, then hang indefinitely on the splash screen. No errors, no prompts—just that familiar startup screen, stuck.

What caught my attention wasn’t just the issue itself—it was the fact that this happened on two separate computers, at nearly the exact same time. Strangely enough, the user’s phone was still receiving mail perfectly, so the issue clearly wasn’t with the email account or mail server.

Diagnosing the Usual Suspects

My first step was to run SCANPST.exe, Microsoft's Inbox Repair Tool, which checks the OST (Offline Storage Table) files used by Outlook in cached mode. Both systems reported errors in the OST files. I repaired them—yet the problem persisted.

It wasn’t until I created new Outlook profiles on both systems that things went back to normal. Outlook opened instantly, mail started syncing, and everything worked just as it should. Problem solved... but the mystery remained.

Theories: What Could Cause Synchronized Profile Corruption?

After reflecting on this, several plausible causes emerged:

• Server-Side Mailbox Corruption: A single problematic email, calendar invite, or rule could have synced from the cloud to both systems, corrupting the OST files during download.

• Bad Outlook Update or Add-In: If both systems received a recent Outlook patch or had a problematic add-in, it could have triggered the same crash pattern.

• Shared User Profile Settings: If the user has roaming profiles, corrupted Outlook settings could follow them between machines.

What’s especially interesting is that mobile clients—which use lighter, stateless protocols—continued working, reinforcing the idea that the issue was tied to how Outlook for Windows handles caching and profiles.

Lessons Learned

1. Outlook Profiles Can Be a Single Point of Failure
   When in doubt, start fresh. Rebuilding a profile often resolves weird sync and crash issues.

2. Don’t Trust the OST File Too Much
   Even if SCANPST says it's “repaired,” corruption may persist until the OST is completely rebuilt.

3. Symptom Sync Doesn’t Always Mean Hardware Sync
   Two machines failing in the same way isn’t always coincidence—it could point to a shared mailbox or software behavior.