Stop obsolete addresses from appearing in Messages

Re: How do I stop obsolete addresses from popping up in Messages

You may want to start by ensuring all addresses in your Contacts app are up-to-date, and deleting any old ones.

See how to: Update contact information in Contacts on Mac - Apple Support

1. Go to the Contacts app  on your Mac.
2. Select a contact, then click Edit at the top of the window.

Do any of the following:

• Edit information in a field: Click a field, then enter your changes.
• Remove a field: Delete the information in the field, or click .

When you’re finished, click Done.

___________ (If needed: There's more info. in the above linked article.)

Then try this:

Begin composing a message to the person whose old address is appearing in your messages.

When / if the address appears, tap the (i) for info. button next to the address.

Tap "Remove from Recents"

If it doesn't work for you in the Messages app / try it in the Mail app (My MacOS is an earlier version)

Thank you kindly! Seems like the address was removed from "Recents" using (i) info, but the change just hasn't fully reached that Contacts listing yet.

Restarting your Mac (Apple Menu > Restart) will likely restore order. (Restarting deletes temporary files, may update recent setting changes etc., re-establishes connections, and more.)