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 Shell 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:Y54kpX5g:
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 output here unredacted or incorrectly redacted may 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 unsuccessful 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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