A lot of users use POP3 and SMTP to send and receive emails from their yahoo email account. I recently had a customer who was using Outlook to get emails via POP from Yahoo and Outlook started requesting a username and password. I verified the username and password were correct by login into yahoo.com and they worked fine. The settings in Outlook all seemd fine aswell and as a precaution I reset the password which also made no difference.

Analysis

When I analysed the errors sent back while sending an email using the Yahoo system a MR1212 error was highlighted and this let me to idetify the problem and solution. I used SMTP Diagnostics to generate the email reports.

Failed email report

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SMTP Diagnostics Report
Trial version. Visit http://www.smtpdiagnostics.com/ for more information.
12/01/2017 13:03:10
Elapse time: 0:00:03.422
....................
Email address: not-real@yahoo.co.uk
Outgoing mail server (SMTP): smtp.mail.yahoo.co.uk
Port: 465
My outgoing server (SMTP) requires authentication
  User name for outgoing server (SMTP): not-real@yahoo.co.uk
  Password for outgoing server (SMTP): ***********
Subject: [SMTP Diagnostics] Send Test
Message:
Send test from SMTP Diagnostics.
....................
Connecting to mail server.
Connected.
220 smtp.mail.yahoo.com ESMTP ready
EHLO Dell
250-smtp.mail.yahoo.com
250-PIPELINING
250-SIZE 41697280
250-8 BITMIME
250 AUTH PLAIN LOGIN XOAUTH2 XYMCOOKIE
AUTH LOGIN
334 VXNlcm5hbWU6
bWNnYWZmaWdhbnNAeWFob28uY28udWs=
334 UGFzc3dvcmQ6

Successful email report

....................
SMTP Diagnostics Report
Trial version. Visit http://www.smtpdiagnostics.com/ for more information.
12/01/2017 13:03:54
Elapse time: 0:00:00.641
....................
Email address: not-real@yahoo.co.uk
Outgoing mail server (SMTP): smtp.mail.yahoo.co.uk
Port: 465
My outgoing server (SMTP) requires authentication
  User name for outgoing server (SMTP): not-real@yahoo.co.uk
  Password for outgoing server (SMTP): ***********
Subject: [SMTP Diagnostics] Send Test
Message:
Send test from SMTP Diagnostics.
....................
Connecting to mail server.
Connected.
220 smtp.mail.yahoo.com ESMTP ready
EHLO Dell
250-smtp.mail.yahoo.com
250-PIPELINING
250-SIZE 41697280
250-8 BITMIME
250 AUTH PLAIN LOGIN XOAUTH2 XYMCOOKIE
AUTH LOGIN
334 VXNlcm5hbWU6
bWNnYWZmaWdhbnNAeWFob28uY28udWs=
334 UGFzc3dvcmQ6
bWNnYWZmczEyMzQ=
235 2.0.0 OK
RSET
250 flushed
MAIL FROM: <not-real@yahoo.co.uk>
250 OK , completed
RCPT TO:<not-real@yahoo.co.uk>
250 OK , completed
DATA
354 Start Mail. End with CRLF.CRLF
.
250 OK , completed
QUIT
Disconnected.
221 Service Closing transmission
....................

Cause

Yahoo have recently changed their account security settings disabling POP and SMTP

We may block email applications that use a no longer recommended sign in method from accessing Yahoo accounts. We recommend upgrading to an app with up-to-date sign in security measures to better protect your account.

Solution

We have to enable POP and SMTP but the setting is not named that well.

Yahoo Account --> account security --> allow apps that use less secure sign-in

Looks like this

Should look like this

Links

• Ways to securely access Yahoo Mail | Yahoo Help - SLN27791 - says "While changing or upgrading your third party applications, you can temporarily give them access." which allows POP3 to work again
• Yahoo’s “Less Secure App” Setting – Context.IO