If you are logging into your Fastmail account from a browser on a PC (and not using an email client), I agree with the suggestion that the choices you are given come from your Contacts list. Here is how new people are added to the
Autosaved address book group in Contacts automatically:
- Navigate to Settings>Customize>Preferences>(Show advanced preferences at the bottom)>Compose & Reply>Auto-save contacts
- You can choose to automatically add new contacts (to your Autosaved address book group) when you send them an email.
To search for an address so you can remove it from your Contacts, be sure to first select All Contacts at the upper left. The entry might be in the Autosaved group and/or other contact groups.
Bill