What are your settings? Yahoo accounts use these ones:

imap.mail.yahoo.com on 993, smtp.mail.yahoo.com on 465; SSL/TLS, authentication = OAuth2, User Name = email address.

Already using the same settings.. it works for POP server but ask for password for smtp and do not accept the password.

The smtp should use the same password as the one used to receive mail, as long as the sending account and the associated smtp server have the same User Name (email address). In Account Settings, select an account in the left pane, then Outgoing Server (SMTP) in the right pane. Click Edit SMTP server... to check that the User Name in the selected smtp is the same as the User Name for the account in the left pane.

If it's set up correctly, you should only be asked once for the account password in the OAuth window when first connecting to the POP or IMAP server. Sending should proceed with the same password and no prompt for a password.

Thanks for your help sir.. problem is solved. actually yahoo mail needs app specific password which i generated from account info> account security > Generate and manage app passwords.. and after entering this password mail start working.. :)

With most providers that use OAuth2, app passwords are only required if the authentication method in TB is 'normal password', and if OAuth2 isn't supported, an app password is used when two-step verification is set on the account. Check that OAuth2 is selected for both the incoming and outgoing Yahoo servers.