Ignition Edge uses the username from the Email Settings as the "from" address when it sends out alarms. In our case, the username to log into our SMTP server is just a name - no @, no domain name. So the email send fails with a "no domain name specified" error.

Please add a field in the Edge Email Settings (or in the tag's Alarm settings) for a separate "From" address rather than just using the username field.