Mail not Sending in Outlook or Thunderbird Apps...

[Mykol]

The Microsoft Outlook & Thunderbird Web Apps have, without warning, begun failing to send emails; keep requesting authentication credentials.

The credentials are clearly correct as I am able to receive emails. And before you ask, I have gone through the Renew App Password process in order to eliminate that possibility.

Likewise, the server settings (name; ports; encryption method) as these have not been changed and worked up to a few days ago…

My Android App works without issue; likewise VM Webmail.

Very odd; very frustrating as Outlook is my main Mail App…

[用心棒]

It would be helpful to see what, if any, error code is returned by the SMTP server in this situation. From a desktop or laptop device open a Command Prompt in Window or otherwise a Terminal. and enter the following where username:password is replaced with your email address and password, i.e. richard.branson@virginmedia.com:rotavator-racecar-tenet-repaper:

curl -v smtps://smtp.virginmedia.com -u username:password

Do not post the resulting output here but instead review it for possible reported causes, i.e. VM error code; choosing to ignore this advice and posting the unredacted or incorrectly redacted output here will likely reveal your email address, password and / or public IP Address.

FYI if there is no issue then you should see the following output from the curl command:

⋮
> AUTH PLAIN
< 334 
> [Redacted]
< 235 2.7.0 SMTP350 Authentication successful for user [Redacted]
> HELP
< 214-2.0.0 This is cmsmtp ESMTP service help
214-2.0.0 This is cmsmtp ESMTP service help
< 214-2.0.0 To contact postmaster send email to postmaster@virginmedia.com.
214-2.0.0 To contact postmaster send email to postmaster@virginmedia.com.
< 214-2.0.0 For local information send email to Postmaster at your site.
214-2.0.0 For local information send email to Postmaster at your site.
< 214 2.0.0 end of HELP info
214 2.0.0 end of HELP info
* Connection #0 to host smtp.virginmedia.com left intact

Otherwise an unsuccessful result will look similar to the following:

⋮
> AUTH PLAIN
< 334 
> [Redacted]
< 525 5.7.13 Authentication Denied (VM320)
* Closing connection 0
* TLSv1.2 (OUT), TLS alert, close notify (256):
curl: (67) Login denied

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[Mykol]

Thanks for your response. Authentication was successful and when I tried Outlook again, it successfully sent some emails. I have no idea whether that was because of using that command or just a coincidence: sending emails through Outlook/Thunderbird has been quite flaky recently... 

[用心棒]

It is a coincidental. Good to read the issue resolved itself; should it reoccur consider using the curl command to determine the cause.