HOW TO delete an email address from GMail auto-complete list without deleting Contact
Supposedly friendly features like spell-check & auto-completion can be a bane sometimes. Imagine if your boss & best friend share the same name & you excitedly send a very private message to the boss instead of the friend because GMail cleverly fills the email address while you type a few characters of the name. If such a scenario rings a bell, here is one option to prevent GMail from supplying names you don't want to see in the email auto-complete list that appears while composing a mail. The easy way is to delete the contact. But if you want to prevent an email address from showing up in GMail auto-complete list when you try names in the To:, CC: or BCC: fields, then you can consider moving the email address from the Email field in the form for that Contact to the Notes field. click on image to enlarge