Unlike before with Thunderbird where you could just create one Outgoing SMTP server setting and use it with all of your email accounts, I had to create a new SMTP server setting for each of the email addresses that were ported over to Yahoo. When you go into Account Settings, scroll all the way to the bottom and select "Outgoing Server (SMTP)" then click Add and make a new SMTP server setting for each email address now with Yahoo.
The settings need to be:
Description: any unique name you want
Server name: smtp.mail.yahoo.com
Port: 465
Connection Security: SSL/TLS
Authentication method: OAuth2 Note: I seem to recall this option didn't show up until I saved the setting then went back into it.
User Name(you must put the full email address here now): whateveryouraccountnameis@cox.net
Then go into the Account Settings of each individual account and at the bottom select the associated SMTP server you create for that account.
Repeat for each email account ported to Yahoo.
Sending emails problem---- Got it finally. On account settings, while the account name should be yourname@yahoo.com, down below under Default Identity, email address is (actually remains) yourname@cox.net and I think the same is true for reply-to address. Once I changed that, I was able to send emails just fine. Somehow I assumed you had to replicate the yahoo.com address in those locations. Sigh, what a slog! Tomorrow, I need to attack my iphone and get that to talk to Yahoo; hopefully that won't be as awful as my desktop/Thunderbird struugle.
