I sent surveys to internal colleagues in a test phase. All went as planned. When it came time to send to external clients, although the survey was marked as sent with a time and appropriate icons, none were received. It appears to be a setting or a firewall issue. I have my IT people working on the firewall. Can anyone help with the settings?

The fact that respondents have not recieved your emails, there can be many, many reasons.

What are your settings in the email settings?
To what kind of emails have you sent the invitations?