Outlook – How to disable security alerts for self-signed certificates in Outlook 2010

certificatemicrosoft-outlook-2010ssl

I've just switched from using unencrypted SMTP and IMAP for mail in Outlook 2010. My mail is hosted on a shared hosting setup and not my own, dedicated server.

The certificate issued by the server is self-signed. I am fine with that and I am completely aware that it is self-signed.

However, Outlook issues a warning about the certificate each time it opens.

I have tried installing the certificate, as Matthew Williams suggests in his answer, but this does not result in the warning being dismissed.

How can I permanently disable/ dismiss this warning?

Best Answer

You can install the certificate so it's allowed without issue. Within the security dialogue box click view certificate then install certificate. If you require assistance when setting up the certificate Microsoft provide a nice guide you can follow.

http://support.microsoft.com/kb/2006728

Hope that helps.

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Outlook – How to Disable or Bypass Outlook Certificate Warning

Instead of using an HTTP proxy, I suggest you set up Network Address Translation, to move IP packets at the IP layer. This will pass through the SSL connection without decrypting it at the gateway PC, and eliminate the security warning. Basically Outlook is telling you that your gateway PC is trying to perform a man in the middle attack, which it basically is.

The way SSL (encrypted) connections work is, it's perfectly fine if someone is sitting between you and the server you're communicating with and is simply viewing the encrypted traffic. The protocol is designed to accommodate situations where other computers (trusted or not) can see your encrypted traffic. But if other computers can see your encrypted traffic, such as with an HTTP proxy, the protocol is immediately aware of that fact, and flags the connection as insecure.

You can set up Network Address Translation on the gateway PC (the one connected to the EvDO modem) using for example, Windows Internet Connection Sharing. This allows the other PCs connected to have a private IP address on a private subnet that all routes out to the EvDO modem eventually. It basically treats your gateway PC as a router. (Note the term "gateway" refers to a box that performs router and/or firewall-like functions in order to push traffic to and from another network; in this case, the public Internet).

Guides for setting up Windows ICS are exhorbitantly common, not only on SU but also in the Microsoft knowledge base and Windows help. Please explore some of the existing resources along these lines prior to asking for help on how to set up ICS.

Your research regarding certificates is correct. There IS technically a way to induce a silent man in the middle attack, by trusting a Root CA for which your freeproxy server has a signing key. I don't know if the actual freeproxy program is able to encrypt the traffic on a domain basis, but programs such as Burp definitely can, and there are existing guides out there explaining how to set it up (on Burp's site at portswigger.net).

However, ICS is a solution that is much more flexible and does not involve this configuration hassle, so I highly recommend it.

Outlook shows certificate security warning in local LAN although certificate is only associated to IIS

Your certificate is for webmail.example.org. If you're connecting to your Exchange server via server.domain, then the name will not match the common name in the certificate, thus the error.

You either need a certificate that includes both names or you always have to use the external name (even when on the LAN).

To make sure your clients use the external connector for your Exchange services, here are a few commands that may help:

EXCHANGE-SERVER is the hostname of your Exchange server
exchange-server.yourdomain.com is the externally visible name of your Exchange server

Commands

Set-ClientAccessServer -Identity EXCHANGE-SERVER -AutoDiscoverServiceInternalUri https://exchange-server.yourdomain.com/Autodiscover/Autodiscover.xml

Enable-OutlookAnywhere -Server EXCHANGE-SERVER -ExternalHostname "exchange-server.yourdomain.com" -DefaultAuthenticationMethod "Basic" -SSLOffloading:$False

Set-OABVirtualDirectory -identity "EXCHANGE-SERVER\OAB (Default Web Site)" -externalurl https://exchange-server.yourdomain.com/OAB -RequireSSL:$true -InternalUrl https://exchange-server.yourdomain.com/OAB

Set-WebServicesVirtualDirectory -identity "EXCHANGE-SERVER\EWS (Default Web Site)" -externalurl https://exchange-server.yourdomain.com/EWS/Exchange.asmx -BasicAuthentication:$True -InternalUrl https://exchange.haseke.de/EWS/Exchange.asmx

Best Answer

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Outlook – How to Disable or Bypass Outlook Certificate Warning

Outlook shows certificate security warning in local LAN although certificate is only associated to IIS

Commands

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