NOTE: This article is for informational purposes. ISN is not affiliated with Yahoo in any official capacity and cannot help you troubleshoot anything else in your Yahoo account.
ADDITIONAL NOTE: Yahoo Mail owns and runs email services for SBCGlobal and AT&T, however, the enable less secure apps button does not exist or work for those email accounts. Any email coming from @sbcglobal.net or @att.net cannot be used for sending email in ISN via SMTP.
Yahoo mail now requires you to enable less secure apps to work with ISN for SMTP.
Sign in to Yahoo Mail.
Turn on Allow apps that use less secure sign in.
Confirm your identity
You're all set! See the screenshots below for each step.
Yahoo will automatically save this for you, there is no SAVE button.