Server certificate warning when sending email (from Outlook)

[rjpreston]

When i attempt to send an email using Outlook 365 desktop app, i get a warning that the mail.btinternet.com server SSL certificate has expired.

The exact wording is "This certificate has expired or is not yet valid. Issued to: mail.btinternet.com. Issued by DigiCert Global... Valid from 01 Mar 2023 to 01 Apr 2024

Outlook then asks whether i want to continue using the server to send the email.

I havent seen* any other messages on this forum about this error, so i assume it is either a server fault that has just occured, or that there is a problem with my setup that is causing the error somehow (although email has been working fine up to now and i havent changed anything my end.

(* Editted: This problem from 2 days ago could well be the same issue.Outlook 365 (new Outlook) no longer working with B... - BT Community A server certificate problem could be the underlying cause for both my problem and this other one.)

[cert1002 · Accepted solution]

I had a very similar problem and I managed to fix it this morning. It started yesterday and it was the first time I had seen it. I use Outlook 2010. I could receive mail but sending mail caused a popup box with 'Internet Security Warning' Your certificate is not working, View Certificate, and the sort of text you note.

Within account settings for this mail program there is an option labelled 'Repair'. I clicked on that and Outlook did an auto reset. It checked settings and sent a test message. I bounced emails between different accounts on other services and that seemed fine. I rebooted and retested. I can now send/receive with no popup warnings.

I hope this functionality is present in your desktop app.

[rjpreston]

Thanks. I’ll have a look after work.

[JPWarwick]

I have had the same problem for the last couple of days. I am running Outlook 2019 on a Windows 10 PC.  I've tried the Repair process and it hasn't solved the problem - I'm still getting the pop-up when trying to send emails.  What is odd is that it says the certificate expired on 1st April but I've only been getting the pop-up for the last three days.  Does anyone know if it's possible to get and import a new current certificate?

[rjpreston]

Just to confirm that since following cert1002's suggestion i have not had any reoccurrence of this error.

NB. i did the account "repair" via "Control Panel > Mail (Microsoft Outlook)" rather than in Outlook itself.

[JPWarwick]

The problem has gone away now on my PC so either the repair fix worked or BT changed something else in the background to resolve this problem!