topic Re: Internet Security Warning - View Certificate in Email

Internet Security Warning - View Certificate

DaveM54 — Tue, 27 Jan 2026 12:59:29 GMT

Since the recent Windows 11 update KB5074109 which has now been acknowledged as causing all sorts of problems when using Outlook Classic in Office 2021.

I have virtually had to rebuild all of my email accounts in Outlook so I could download my emails.

I have now got everything working, the only problem I am having is when it comes to downloading my Lineone emails I get a pop up Internet Security Warning that says "The server you are connected to is using a security certificate that cannot be verified. The target principal name is incorrect". It then gives me a button to view the certificate. And then a line which says "Do you want to continue using the server" then there are two more buttons saying yes or no. If I press the yes button my emails then download ok. I don't get this warning with my two talktalk email addresses or my Tiscali email address. As far as I can see I have used the same settings on all of my accounts.

I since tried uninstalling the dodgy Windows update as suggested by posts on Microsoft forums but it has made no difference.

I have seen this problem before when I set up my new laptop about 3 years ago I think but I can't remember which account it was on.

I have enclosed screen dumps of my settings and the security pop up.

Re: Internet Security Warning - View Certificate

Mandisa-TT — Tue, 27 Jan 2026 13:13:01 GMT

Hi @DaveM54

I’m really sorry to hear about the trouble you’ve had since the recent Windows 11 update. We will look into your query and assist you.

Re: Internet Security Warning - View Certificate

Mandisa-TT — Tue, 27 Jan 2026 13:32:23 GMT

Can you confirm if Lineone Webmail is working normally at https://apps.talktalk.co.uk?

Re: Internet Security Warning - View Certificate

DaveM54 — Tue, 27 Jan 2026 14:01:57 GMT

Yes I have just tried logging into my Lineone webmail and it is working ok.

When once I press the yes button on the warning my Lineone emails download ok.

Re: Internet Security Warning - View Certificate

Mandisa-TT — Tue, 27 Jan 2026 14:03:47 GMT

@DaveM54

It’s good to hear that you’re able to access your Lineone Webmail without any issues — that confirms the mailbox itself is working normally. The fact that your emails download in Outlook once you press “Yes” also tells us the account is active and connecting correctly.

The warning you’re seeing is linked to Outlook checking the security certificate, and it usually appears when the account is still using older Lineone server names or when Outlook is expecting the certificate to match the TalkTalk hostname.

Re: Internet Security Warning - View Certificate

DaveM54 — Wed, 28 Jan 2026 10:33:59 GMT

So how do I resolve this? I don't get the pop up with my talktalk and old tiscali email addresses.

Re: Internet Security Warning - View Certificate

mandisa1-TT — Wed, 28 Jan 2026 11:21:03 GMT

I would love to assist you however my resources are limited, as Outlook is a third-party APP.

Re: Internet Security Warning - View Certificate

DaveM54 — Tue, 03 Feb 2026 16:32:11 GMT

It looks as if I have managed to solve this problem. I changed the in and out mail servers from lineone.net to talktalk.net and the message stopped coming up. Just out of interest I also changed my tiscali.co.uk in and out mail servers, which were working without the message popping up, to talktalk.net and that worked as well.

Re: Internet Security Warning - View Certificate

mandisa1-TT — Tue, 03 Feb 2026 16:35:27 GMT

Thank you so much for the information @DaveM54 it will be useful to anyone else experiencing the same issue, accessing their Emails via Outlook.