Fix Outlook Autofill Not Working - Easy Solution

First Check the AutoComplete Setting Is Switched On

Outlook remembers the people you email and offers their names as you type — that memory is called the AutoComplete List. Everything else is wasted effort if its one checkbox is off, so check it first:

1. Open classic Outlook and go to File > Options > Mail.
2. Scroll to the Send messages section.
3. Tick Use AutoComplete List to suggest names when typing in the To, Cc, and Bcc boxes.
4. Click OK, close Outlook fully and open it again.

This box sometimes gets unticked by an update, a repair, or someone cleaning up settings. Checking it takes twenty seconds and fixes a surprising share of cases on its own.

Test It the Right Way Before Digging Deeper

AutoComplete only remembers people you have actually emailed from this profile, and it needs a few letters before it can match:

1. Open a new email and click in the To field.
2. Type the first two or three letters of a name you email often, then pause a second.
3. If a drop-down appears, AutoComplete is alive — the earlier test was just a name it does not know yet.
4. If nothing appears for a person you emailed yesterday, continue to the next fixes.

Restart the AutoComplete Cache File (the Real Fix)

In classic Outlook the suggestions live in one small cache file. When that file gets damaged, suggestions stop even though the setting is on. Restarting it is the standard fix:

1. Close Outlook completely — check the system tray so it is not still running.
2. Press Windows + R, paste this folder path and press Enter:

%LOCALAPPDATA%\Microsoft\Outlook\RoamCache

3. Find the file whose name starts with Stream_Autocomplete_ and ends in .dat.
4. Rename it to the same name plus .old at the end — do not delete it.
5. Open Outlook. It creates a fresh, empty cache file and suggestions start working again.

Be clear about the cost: the fresh file is empty, so old suggestions do not come back on their own. They rebuild one by one as you email people. The renamed .old file keeps the old data on disk, so nothing is destroyed — and it can be restored or carried to another PC later.

If It Still Fails, Test with a New Outlook Profile

If the cache restart did not help, the damage is usually in the profile itself rather than in the list:

1. Close Outlook, then open Control Panel > Mail (Microsoft Outlook) > Show Profiles.
2. Click Add, create a new profile and add the same email account.
3. Set Always use this profile to the new one and open Outlook.
4. Send one or two test emails, then type a few letters in the To field.

If suggestions work in the new profile, the old profile was the problem — keep the new one. Your mail itself is untouched by this test, because IMAP and Microsoft 365 mail lives on the server.

What Not to Do — the Empty List Button