How do you get a name remembered in the "TO" line of an email

[Frank L]

When I write an email using outlook in the "TO" I am able to type the first
letter of someones name and a dropdown list will come up and let me slect the
name and address I want. I had to delete an old address of someone and now
the name and email address will not come up when I type the first letter.
Anyway to get it in again?

Thanks,

Frank