First are you using webmail viewed and sent via your browser ?
Or are you using an email program, if so what program ?
Disabling the web shield 'shouldn't allow email to be sent,' as the email shield should be scanning outbound email on the SMTP port 25. If using port 80 for SMTP then the web shield redirects that port so it can scan the HTTP traffic (which it expects on that port), the problem comes when it receives SMTP protocol traffic when expecting HTTP traffic.
I suspect that you may be using a GoDaddy email account (seen this before in the forums) and for the weirdest of reasons they have you use port 80 (the internet HTTP port) to send your email ?
This is against standard non-ssl port/protocol use, email ports are generally POP3 port 110 (POP protocol), SMTP port 25 (SMTP protocol). Secure email usually uses different ports, 993 for secure POP3 and SMTP Ports, 587 or 465 for secure SMTP.