Hi Thunderbird updated its authentication for Yahoo and AOL accounts to a more secure protocol called OAuth2 with PKCE. Because of this change, your old login "tokens" or passwords saved in Thunderbird are no longer valid, and you likely need to re-authenticate. NEW! Update to secure PKCE authentication settings, March 2026 1. Update the "'''Authentication Method'''" for the POP3 or IMAP mail account. Go to '''Settings > Account Settings >''' '''Under '''your AOL account on the left, select '''Server Settings'''. '''Change '''Authentication '''to OAuth2'''. '''Repeat '''this for the Outgoing Server (SMTP) settings. 2. Check Thunderbird has cookies enabled. Click Thunderbird app menu '''☰ > Settings > Privacy & Security'''. Tick ✓ '''Accept '''cookies from sites. Click '''Exceptions…''' next to Accept cookies from sites to make sure you are not blocking cookies from sites such as yahoo.com, aol.com or att.com. More info [[OAuth2 Authentication for Yahoo, AOL and ATT]]