SEMS (Symantec Encryption Management Server) Web Email Protection (previously known as Web Messenger) prior to release 3.3.1 MP1 is not compatible with Internet Explorer 11.
Internet Explorer 11 is available for Windows 7 SP1, Windows 8 and Windows 8.1.
If an external user tries to access the Web Email Protection site using Internet Explorer 11 they receive an error message stating "Web Email Protection does not support your browser". The message further states "You may proceed using your current browser" but clicking on the OK button returns the user to the same page so they cannot continue.
The error message is as follows:
Internet Explorer 11 is incompatible with Web Email Protection / Web Messenger in SEMS 3.3.1 and below.
Upgrade to SEMS 3.3.1 MP1.
Workaround for previous versions:
In SEMS 3.3.1 and below, as a workaround, ask external users who access Web Email Protection using Internet Explorer 11 to turn on Compatibility View. To do this, click the Settings icon and select Compatibility View Settings:
From the Compatibility View Settings page, click the Add button to add the Web Email Protection domain to the list of web sites that will use Compatibility View and then click the Close button: