You shouldn’t need to use 10 different email addresses. If all of your websites are hosted on the same account, you can select just one of them as the primary SMTP server and use those details for all your forms.
I’m not sure if Apple allows people to use their outgoing mail server for form submissions if you are wanting to use your mac.com email address, however you could give it a try 
Try the SMTP information for the outgoing iCloud Mail server settings.