Last reviewed on June 28, 2012   —  3 Comments

This hard to understand error means the security certificate your email server is using has expired or is invalid for other reasons.

I'm getting a security warning when I open Outlook. It says: 'The server you connected to is using a security certificate that cannot be verified. A required certificate is not within its validity period when verifying against the current system clock or the timestamp in the file'

That message is saying that the certificate the mail server uses has likely expired.

If you are the administrator, you need to install an updated certificate; if you are an end-user, you need to speak to your admin. You can't hide the warning or turn it off, but in all likelihood, it's safe to OK it and connect to your mail server.

The message made perfect sense to me but not to the people who asked about it, so I asked a couple of family members who aren't into technology what they thought the message was trying to tell them and what they would do if it came up while they were on the computer. Their answer: it "hurt" to read it and they'd ask me to look at it. I guess that proves it's a poorly written, overly technical error message.

Target Principle name is incorrect

I have a SSL IMAP email account that I just setup in Outlook. Every time I run the program I get a popup: "Internet Security Warning" The server you are connected to is using a security certificate that cannot be verified. The target principle name is incorrect. View Certificate. The certificate is self signed so I always just click Yes to continue using the server/email account, but how do I get Outlook to remember?

Certificate warning

This warning indicates the server name does not match the name in your account settings, or in the case of Exchange server, that the address in the autodiscover file does not match the address the server is using. This is a common problem when the administrator uses self-published certificates.

If you can't change the server name you use in Outlook, you can publish the certificate in the Certificate store to reduce the frequency of the alert. In the Trusted Publishers folder should suffice or use the automatic setting. This probably won't totally eliminate the dialog, but you'll see it less often, usually only when you restart Outlook.

To publish the certificate, click View Certificate then Install Certificate. Choose Current user, click Nest then Install.

Install the certificate

For example, in the dialog in this screenshot, the server certificate was issued to but I'm using as the server name in my account settings.


  1. Terry HelpMe says

    Wow. This didn't help at all. Publish what certificate in what certificate store? OMG. I think it has something to do with my incoming and outgoing servers as I am with AT&T but have and old sbcglobal email address. I think I'd rather kill myself than call AT&T.

    • Diane Poremsky says

      target principle name error means the certificate was issued for different server names than you use for pop3/imap and smtp. You'll get it if you use as the server name and redirect you to att (or yahoo) servers. Click view certificate then Install Certificate - choose current user, the click Browse and install it in the Trusted Publishers folder.

  2. Diane Poremsky says

    As an FYI, after you publish the certificate, you may still receive the 'do you want ot connect' dialog, but it should be less frequent.

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