By default (when this option is set to No) Virtualmin will display a warning if you try to create two SSL-enabled websites on the same IP address without a certificate that can be used for both domain names. This is necessary because the HTTTP protocol did not originally provide any way for the web server to select the correct certificate in this situation.

However, an improvement to the SSL protocol called SNI (server name identification) solves this problem, by allowing the web browser to send a hostname before SSL certification selection is done. All modern browsers support this extension, but IE 6 and below and all IE versions on Windows XP do not.

Selecting Yes for this option will remove the warning when two SSL sites are on the same IP address, based on the assumption that all web browsers connection to your sites support SNI. If a browser without SNI support connects, the user will see a warning about a mismatched certificate.