Outlook profiles store their account configuration in the Windows registry — email address, mail server, delivery settings — and that structure has been stable since roughly Outlook 2000. Reading it directly is a normal, well-worn approach for tooling that needs to inspect what's configured without going through Outlook's own automation layer.
Most of those values are stored as plain strings (REG_SZ), and reading them is exactly as boring as it sounds: open the key, call GetValue, get a string back. We had that working reliably against modern Outlook installs. Then a real Outlook 2010 install came through a migration batch reporting zero accounts configured — on a machine we could independently confirm had two active POP3 accounts, mail actively flowing.
The cause was almost invisible in code review: on that install, several of the account fields — including the email address itself — were stored as REG_BINARY rather than REG_SZ. Calling .ToString() on a byte array in .NET doesn't throw and doesn't return an error string. It returns the literal text "System.Byte[]". That string obviously doesn't contain an @, so our validation logic — reasonably, given what it knew — treated the account as not present at all and moved on silently.
No exception, no warning, no failed request. Just a correctly-running scan that returned an answer that looked exactly like "nothing configured here" instead of "I don't know how to read this."
The fix was to stop assuming the registry value's type and check it explicitly — read it as a string if it is one, and if it's binary, decode it as UTF-16 or ASCII text before validating. We already had a helper written for exactly this in the codebase, from an earlier pass; it just wasn't wired into the one code path that needed it.
The broader lesson wasn't really about Outlook. It's that "returns cleanly with no error" and "returns the right answer" are different claims, and code that reads external data — a registry value, a file, an API response — should be suspicious of the first one until it's checked the second.