The security certificate warning in Outlook: what it means and how to stop it

E-mail·· 63 views· 3 min read

The short answer: the warning “The server you are connected to is using a security certificate that cannot be verified” appears when the server name you typed in Outlook does not match the name on the certificate, or when the certificate has expired. In most cases it is fixed by using mail.yourdomain as the server, both incoming and outgoing.

Why it appears

Symptom Most likely cause
You typed the machine’s name, or an IP, as the server The certificate is issued for your domain (mail.yourdomain), not for the server’s technical name or an IP number. The name does not match and Outlook warns.
You use mail.yourdomain and the warning appeared suddenly Your domain’s certificate may have expired or be renewing. If the domain does not point to us (DNS elsewhere), automatic renewal can fail.
The warning appears only on one network Some office networks and some antivirus programs inspect connections and present their own certificate. It is not our server.
The computer’s date is wrong With the wrong time, a valid certificate looks not yet valid, or expired.

Making the warning go away

1 See what the warning says: press View Certificate. The “Issued to” field shows the name the certificate is valid for.
2 Put that name in Outlook: in File > Account Settings > Change, use mail.yourdomain for incoming and outgoing (replace “yourdomain” with your domain), with IMAP 993 SSL/TLS and SMTP 465 SSL/TLS or 587 STARTTLS.
3 Check the computer’s date and time and fix them if they are wrong.
4 Test on another network. If the warning disappears, the network or the antivirus is stepping into the connection: switch off its “encrypted connection scanning” for e-mail.
5 If the certificate has expired for your domain, tell us: we check the automatic certificate on the server side.
Do not press “Yes” forever without knowing why. Accepting the warning keeps things working, but if the cause is a network stepping in, you are accepting that someone can see the connection. Fix the server name and the warning goes for the right reason.
The same goes for the phone: if the warning appears there too, use mail.yourdomain in the account settings. The guide is in other e-mail apps on your phone.

Warning still there with mail.yourdomain? Send us a screenshot of the certificate (“View Certificate”).

Open a support ticket

SEE ALSO

Common Outlook errors: 0x800CCC0E, password prompts and more

Autodiscover and autoconfig: how Outlook and your phone find the mailbox settings

Outlook shows Disconnected or Working Offline: how to get it back online

How to set up your e-mail in the new Outlook for Windows

How to set up your e-mail in Outlook 2016 and 2019

Other e-mail apps on your phone: Gmail, Samsung Email and Outlook, with the same settings

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