I think that AOL requires a APP password when using email clients on a PC. I believe you must go to the AOL site and select the security page and can set up the APP password there. See this page for more info: https://help.aol.com/articles/Create-and-manage-app-password

Following the suggestion to not include a password when generating a new account, I now have the new account (same email address as the old one) appearing at the bottom of my list.

I tried sending a message from the IMAP account and got a sending failed-enter password message. I logged into AOL, got the aol-generated password, and pasted it into the password field for the new account. I didn't get an error when sending a test message (to a gmail account), but the message hasn't shown up in the gmail account, either.

When I ask TB to get new messages, they're showing up in my old pop3 account, and not the IMAP account.

Don't use app passwords with AOL. Set the authentication method to OAuth2 for incoming and outgoing, remove the entries from Saved Passwords in Settings, restart TB, enter the account password in the OAuth window to allow access.

Authentication set to OAuth2 in & out. Removed entry from Saved Passwords, restarted TB.

Tried to send email. Got request for account password. Entered my AOL password. Now popup "Login to server smtp.aol.com with username Paul.h.brown@verizon.net failed"

If the authentication is OAuth2, you shouldn't see the 'normal password' authentication request for a password - you should see a browser-like window. That works for @aol.com accounts, but for Verizon accounts hosted on AOL, the outgoing server is supposed to be smtp.verizon.net, not smtp.aol.com.

https://help.aol.com/articles/how-do-i-set-up-other-email-applications-to-send-and-receive-my-verizon-net-mail?guccounter=1

In that case, OAuth2 should work for the incoming imap.aol.com, but for the outgoing smtp.verizon.net, use an app password with 'normal password' authentication.

https://support.mozilla.org/en-US/questions/1364324

Default outgoing server:

SMTP server Settings Description AOL server name: smtp.verizon.net port: 465

Security and Authentication Connection Security SSL/TLS Authentication: Normal Password User Name: Paul.h.Brown@verizon.net

I sent test messages to one of my gmail.com accounts. The messages show up in my Sent messages when I log into AOL.com on the web, but there is no sent message folder in my new IMAP account on TB. Also, I don't get the test message in my gmail account now.

With my AOL account, sent messages are stored in the Sent IMAP folder, which is specified in Copies & Folders in Account Settings. Check that Sent, not Sent Items, is subscribed. Unfortunately, I can't test the properties of the smtp.verizon.net server, but I would be curious to know if your Verizon account works by sending through smtp.aol.com, with OAuth2 authentication, instead of smtp.verizon.net with normal auth./app password.

I assume you mean your AOL account on TB.

In my new IMAP account on TB, I don't have a Sent IMAP folder. When I go to Account Settings for that account, I see a "when sending messages, automatically" Then checkmarks at

  Place a copy in Sent Folder on paul.h.brown etc
  Message Archives - keep in Archives folder on same account
  Drafts - same
  Templates - same

The only folder that appears under my IMAP account is Inbox. When I attempt to Create a Sent folder in that account, the Sent folder under my pop3 account gets highlighted. Same thing happens when I try to Create a Templates folder: Sent on pop3 account is highlighted.

When I send a message from the IMAP account after changing its outgoing server setting to OAuth2 and smtp.aol.com, I get a "Copying message to Sent Folder that never goes away.

I have a long list of Outgoing Server (SMTP) settings, one for each gmail account and one for the Verizon.net POP3 and IMAP accounts. It appears that nothing happens with OAuth2 authentication.

Oh, and thanks for your continuing to work with me on this.

Could my difficulty lie in having two AOL outgoing servers in my list? - one SMTP.Verizon.net with normal password and one SMTP.aol.com with OAuth2?

In attempting to send a test message from my pop3 account, I get a message: The message could not be sent because the connection to Outgoing server (SMTP) smtp.aol.com timed out. Try again.

Adding to the curiousity, the test message from my pop3 account (with the "Copying message to Sent folder..." message that never goes away, shows up in my gmail account when I access it from the web, but nothing happens when I right click and "Get Messages" in TB on that account.

I closed TB and reopened in safe mode. All my gmail accounts downloaded their messages.

IMAP account incoming imap.aol.com SSL/normal password. Outgoing servers include smtp.verizon.net and smtp.aol.com - both with normal password.

Got a new sync password from AOL.com and entered into both the IMAP and POP3 accounts, and both accounts can now send and receive.

New messages now syncing with IMAP account, but I had to enter the new password from AOL again.

Should I attempt to change to OAuth2, rather than normal password?

The Sent folder need not be added: it should be subscribed by right-clicking the account in the Folder Pane, Subscribe...

Each account should be set to send on an smtp with a matching User Name (email address), even when the other settings are the same. See this topic for an explanation.

The smtp.verizon.net server should work with normal password and an app password. The smtp.aol.com server works with OAuth2, but it might also work with normal password/app password. My question was whether a @verizon.net account can send through smtp.aol.com with OAuth2.

I think to avoid confusion you should do tests with a single account at a time in a test profile. Help/Troubleshooting Info, about:profiles, to create a new profile. Your current profile is unaffected.