Why Outlook Keeps Suggesting the Wrong Email Address (and How to Actually Fix It)
Someone leaves the company, or a client mistypes their own address once, and Outlook never forgets. Every time your team starts typing that name, the wrong address floats to the top of the suggestion list, and eventually somebody clicks it. Invoices go to a dead mailbox. A confidential thread goes to a typo.
Search for a fix and you will find the same advice over and over: delete a file called Stream_Autocomplete.dat, or download a tool called NK2Edit and edit the list by hand. On a Microsoft 365 mailbox in 2026, that advice will usually waste your afternoon. The list is not in that file anymore.
In this article
- Where the Suggestion List Actually Lives
- Fix 1: Remove the Single Entry
- Fix 2: When the Entry Comes Back, It Is Server-Side
- Fix 3: Clearing the Whole List
- Where NK2Edit Still Fits
- Why This Keeps Happening
- Frequently Asked Questions
Where the Suggestion List Actually Lives
Outlook’s AutoComplete list has moved three times, which is why so much of the advice online is wrong for the version you are running.
| Outlook version | Where suggestions come from |
|---|---|
| 2003 to 2007 | A local .NK2 file on the PC |
| 2010 through 2019 | A hidden message inside the mailbox, with a local .dat cache |
| Microsoft 365 on Exchange Online | Microsoft Search on the server, for To/Cc/Bcc suggestions |
That middle row is the one that trips people up. Since Outlook 2010 the authoritative copy has been a hidden message in the mailbox itself, not the file in RoamCache. Microsoft’s own documentation is direct about it: the .dat file is only a cache, and it is not written back to the mailbox when Outlook closes. Delete it, replace it, edit it, and Outlook simply rebuilds it from the server copy. People do this, see the bad address return, and assume the tool failed.
The third row is newer. From Outlook for Microsoft 365 version 2202 onward, a mailbox connected to Exchange Online gets its recipient suggestions from Microsoft Search rather than the local list at all.
Fix 1: Remove the Single Entry
Start here, because when it works it takes five seconds.
- Open a new email and start typing the name in the To field.
- When the wrong suggestion appears, hover over it without clicking it.
- Click the X on the right of that suggestion, or press Delete.
The entry stops appearing. Two caveats worth knowing before you promise a user it is fixed. Sending a new message to that address puts it straight back. And some recent Outlook builds have removed the X entirely, leaving no way to delete one entry from the client. If there is no X, skip to the next fix rather than hunting for it.
Fix 2: When the Entry Comes Back, It Is Server-Side
This is the step almost every article misses, and it is the one that resolves most stubborn cases on Microsoft 365.
If you deleted the suggestion and it returned, the address is probably saved in your mailbox’s Other contacts on the server. Exchange Online quietly saves addresses you have mailed, and that server-side list feeds suggestions to every client you use. Clearing anything on the desktop will not touch it.
- Go to Outlook on the web and sign in.
- Open People (the contacts icon).
- In the left pane, select Other contacts.
- Find the bad entry and delete it.
Because the fix is on the server, it applies everywhere at once: desktop Outlook, the web, and the phone. That is also why the desktop-only fixes feel like they keep failing. They were never touching the right copy.
Fix 3: Clearing the Whole List
If the entry has no X and is not in Other contacts, the remaining supported option is the blunt one.
In Outlook, go to File then Options then Mail. Scroll to Send messages and click Empty Auto-Complete List. You can do the same from a command line with outlook.exe /CleanAutoCompleteCache.
Be honest with the user about the tradeoff first. This wipes every remembered address, not just the bad one, and it rebuilds only as they send mail over the following weeks. For someone who leans on autocomplete all day, that is a genuine productivity hit. We generally reserve it for a mailbox where the list is already a mess.
Where NK2Edit Still Fits
NK2Edit is a long-standing NirSoft utility for reading and editing the AutoComplete list, and it does what it claims. It opens the list, shows every record, repairs corrupted files Outlook refuses to read, merges lists, and exports to CSV or HTML. It runs from a single portable executable and supports command-line scripting.
The honest assessment for a business on Microsoft 365: it is a legacy tool for a legacy storage format, and it is not a supported fix. It genuinely helps in a narrow set of cases, mainly older on-premises or file-based setups, rescuing a corrupted list, or migrating a long autocomplete history to a new profile where losing it would hurt a heavy user. For the everyday “Outlook suggests the wrong address” ticket on Exchange Online, it will often show you a list that has nothing to do with the suggestions the user is actually seeing, because those are coming from the server.
Two things to check before anyone on your team downloads it. It is free for personal and nonprofit use only, so business use requires a paid commercial license after a 14-day trial. And Microsoft’s guidance on the autocomplete stream is to read, modify, and write the whole stream, never a portion of it, and never while Outlook is running. If your environment uses application allowlisting, a portable NirSoft executable will also likely be blocked by design, which is usually the right outcome.
Why This Keeps Happening
A wrong autocomplete entry looks trivial until you count what it costs. Misdirected quotes and invoices. A reply-all thread with client detail going to a former employee’s address that still resolves. Time lost every few weeks to a fix that does not stick, because the technician is clearing a local cache while the real entry sits on the server.
The underlying cause is usually that nobody removed the departed user’s address from the places it was saved, and nobody documented which Outlook build each machine is on. That is ordinary Microsoft 365 administration, and it is exactly the sort of small recurring issue a managed help desk is supposed to close permanently instead of re-fixing every month.
Frequently Asked Questions
Why does Outlook keep suggesting an old email address after I deleted it?
Because you almost certainly deleted the local copy, not the one on the server. On a Microsoft 365 mailbox, the authoritative list lives in your mailbox and the address is often also saved under Other contacts in Exchange Online. Delete it in Outlook on the web under People, then Other contacts, and it will clear everywhere.
Where is the Outlook AutoComplete file stored?
Outlook 2003 and 2007 used a local .NK2 file. Outlook 2010 and later store the list in a hidden message inside the mailbox, with a cache file at %LOCALAPPDATA%\Microsoft\Outlook\RoamCache. That cache file is not authoritative, so editing or deleting it does not reliably change what Outlook suggests.
How do I delete one address from Outlook autocomplete without clearing the whole list?
Start typing the name in the To field, hover over the wrong suggestion without selecting it, then click the X or press Delete. Some newer Outlook builds have removed that X. If yours has, check Other contacts in Outlook on the web first, because clearing the entire list should be the last resort.
Is NK2Edit safe and free to use at work?
NK2Edit is a well-known utility from NirSoft, but it is free only for personal and nonprofit use. Business use requires a paid commercial license after a 14-day evaluation. It is also not a Microsoft-supported fix, and on an Exchange Online mailbox it usually will not resolve the problem, because the suggestions are coming from the server rather than the file it edits.
How do I move the autocomplete list to a new computer?
On Microsoft 365 you generally do not need to. The list lives in the mailbox, so signing into Outlook on the new machine restores it once the mailbox syncs. Manual transfer only comes up on older or file-based configurations, and that is one of the narrow cases where a tool like NK2Edit still earns its place.
Still fixing the same Outlook problems every month?
Small recurring issues like this are a symptom, not the disease. In a free consultation, Braintek will look at how your Microsoft 365 environment is set up and show you which of these repeat tickets should have been closed permanently a long time ago.