Yes, you are breaking the license agreement. With your enterprise license you can only distribute the apps to your company employees If you want to distribute the app to other enterprise employees you should sign it with their enterprise account.
When you create the ipa, there is a checkbox "Save for enterprise distribution", check it and it will create a plist file, then upload that plist and your ipa to any webserver and an index.html with this
<a href="itms-services://?action=download-manifest&url=http://yourweb.com/thePlistYouCreatedBefore.plist">Install app</a></body></html>