When trying to log into Smartermail v10.x with Internet Explorer 11 using any account, Smartermail will not respond.

• To overcome this, go to mail.yourdomainname.com
• Press ALT from your keyboard to open the Menu Bar
• Navigate to Tools

• Click on Compatibility View Settings 
  

• Your domain will be automatically appear under the Add this website field

  

• Click Add and Close

Now, every time a user navigates to mail.yourdomainname.com, IE 11 will default to IE11 Compatibility Mode and the user will be able to login to access their mail.