They come from the autocomplete cache, perhaps from mistyped addresses
perhaps? To delete them, use the up/down arrow to select them and press
delete.

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Milly Staples [MVP - Outlook]
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After furious head scratching, Random asked:
| In Outlook, I have a lot of email addresses that show up in
| Autocomplete that I've never seen before. I'm certain these are not
| people that I know. Where are these coming from?