It's not just people in your address book. People also give their email addresses to the bank, the tax office, their employer, suppliers and all those websites: it's hard to remember all of them.
If you stop the old address suddenly, many of these contacts won't know the new one.
In an effort to let everyone know, several steps are possible. You don't have to do them all.
Get the new address working. Email everyone you can think of and ask them to use the new address in future. Obvious, right.
For a while, have both addresses in your email app. When someone sends to the old address, reply telling them the new address.
For a while, set the old address to forward to the new one. Set up an auto-responder on the old mailserver that nags people to change without you having to do it.
Stop forwarding from old to new, and change the autoresponder to say “I have not received your message. Please send it to my new address.” This can run for months or years.
Stop the old address. Now people who send to the old address get “no such address” messages.
Auto-response messages can be done by Outlook but we don't recommend that. One on the server is more reliable, and still works when your computer is offline.
If your email account is with Riverland Web and Email, we can help with these.