Check your pop mail account settings. https://help.yahoo.com/kb/SLN4724.html

Right click on pop mail account in Folder pane and select 'settings' select: 'Server Settings'

Incoming Mail (POP) Server

   Server Name: pop.mail.yahoo.com
   User Name: full email address
   Port - 995
   Connection Security:  SSL/TLS
   Authentication method: Normal Password

In left Pane at bottom of list, click on 'Outgoing Server (SMTP) select the server and click on 'Edit' check settings: Outgoing Mail (SMTP) Server

   Server Name:  smtp.mail.yahoo.com
   User Name: full email address
   If using Port - 465
      then use Connection Security:  SSL/TLS
   If using Port :  587
      then use Connection Security: STARTTLS

   Authentication method: Normal Password
  click on Ok

click on OK

Close and restart Thunderbird.

Post info showing your current settings. Help > Troubleshooting Information click on 'Copy text to clipboard' in this forum right click in a 'Post a Reply' text box and select 'Paste' remove all info on fonts and printers as they are not needed.

I'm wondering if the option you selected was designed like a 'two step verification'. In which case you may need to generate an application specific password and use that app password in thunderbird instead of your usual password. Very useful if you use eg: a phone to access emails, but otherwise useless if you only use the one computer to access emails via pop.

If you do not use a phone then you may not need the two step verification process, in which case change back to ' Allow apps that use less secure sign in'. Good info here: https://help.yahoo.com/kb/generate-password-sln15241.html

Good morning Toad-Hall, I only access Yahoo Mail via Thunderbird on my Windows 10 PC. The thunderbird account is set up exactly as you have shown (with the outgoing port of 465) and everything works perfectly. ie. I can send and receive via my Yahoo account. My question relates to this: I just happened to log on to my Yahoo account via a web browser (something I very rarely do) and noticed on the 'Account Security' page there are two switches: "Two step verification" (which is off) and "Allow apps which use less secure sign-in" (which is on). So I turned off the "..apps .." switch (meaning only secure apps can access the account). Now Thunderbird can no longer send or receive Yahoo. Question: Can Thunderbird be made to access the 'secure' Yahoo, now or in the future? Regards, Jim

No Thunderbird can not access Yahoo using their new secure login.

Why? because they are idiots and brought in the requirement and then refused to allow us to register Thunderbird. This bug documents the frustration. https://bugzilla.mozilla.org/show_bug.cgi?id=1293958

The short of it is all the coding was done for Googles implementation, all we lack is the key.

Despite the name of the option on Yahoo, there is really not much of a security issue using your old password. Except it is probably the same password you use for Facebook and a dozen other web sites. Or easily guessed like your kids or pets names or birthdates or on the list of the 25 most popular passwords. https://en.wikipedia.org/wiki/List_of_the_most_common_passwords

Kind of an oxymoron when Yahoo claims someone else is less secure!

Basically turn on 'Account Security' "Allow apps which use less secure sign-in" and all should be ok using the same password you used to access your webmail account.

Thank you all for your replies. I now understand that Thunderbird cannot use Yahoo's secure login. Ans all should be well if Yahoo continue to provide the 'less secure' option. Jim