Emails Won't Send

I can't send e-mails from one of my adddresses in Thunderbird. I haven't changed the password on this account. When I try to send an e-mail it won't send and I get the following two messages. Entering the password again makes no difference. What can I do to resolve this? Thanks. Sending of the message failed. Unable to authenticate to Outgoing server (SMTP) smtp.aol.com. Please check the passsword and verify the 'Authentication method' in 'Account Settings | Outging server (SMTP)'. Login to server smtp.aol.com with username xxxxxxxxxxx@aol.com failed. It's OK, this is now resolved. I just needed an app password from AOL/Yahoo. Thanks.