Migrating 80+ shared factory PCs off local POP3 mailboxes
A packaging manufacturer needed roughly 80 Windows PCs — many shared across shifts — moved off standalone POP3 Outlook profiles and onto Microsoft 365, with as little disruption to people still working as possible.
The challenges
- A few of the largest PST files were 90–120 GB. A naive export-then-import pipeline needed up to 3x that size in free disk space at once — original file, backup copy, and a scratch copy for reading — which simply didn't fit on some machines' system drives.
- Several PCs were shared across shifts, with two or three real mailboxes configured in the same Outlook profile. Treating "multiple accounts found" as one ambiguous case risked either blocking the whole machine or, worse, importing one person's mail into a colleague's mailbox.
- A handful of machines were still on Outlook 2010. One had older account data stored in a binary registry format that a naive string read silently misreads as empty — the account looked "not configured" when it very much was.
- One mailbox (about 91 GB, ~23,600 items) failed entirely after successfully processing over 5,600 items, on a single message with malformed internal data. Nothing distinguished "one bad email" from "this mailbox can't be migrated" until we looked at what actually threw.
The approach
We treated each of these as a specific, verifiable problem rather than a generic "retry until it works" one. Disk usage came down by reading the exported backup directly at import time instead of making a third scratch copy, with a short, bounded retry for the one real race condition (a re-export overwriting the same file mid-read). Shared PCs got detected explicitly — when two or more scanned mailboxes each matched their own mapping, every account was migrated in its own isolated pass, with only that account's exported file ever handed to the import step. The registry read was changed to decode binary-encoded account fields instead of assuming plain text. And a single message's import now fails on its own, logged and skipped, instead of unwinding the whole mailbox's progress.
Outcomes
- Per-machine disk headroom needed during import dropped from up to 3x the mailbox size to about 1x, which mattered directly on the 90–120 GB mailboxes.
- Shared PCs migrate each real mailbox independently, with no cross-contamination between accounts on the same machine.
- Outlook 2010 machines with binary-encoded account data are now detected correctly instead of silently reporting no account found.
- A single corrupted message stopped costing an entire large mailbox's progress — the rest of a 90+ GB mailbox keeps importing around it.
- The migration is ongoing across the full device fleet, tracked device-by-device from one dashboard rather than by checking in on each PC individually.