Why does Comcast block jotforms?

I am a Comcast client and I must fill out and receive jotforms from the national headquarters of GCA (Garden Club of America) in NYC. They use your forms on their website and after filling out and sending I am supposed to receive a copy that I need for my records. They never arrive. Upon questioning the GCA contact IT person at HQs, she said Comcast blocks them. As a company, you need to work with Comcast to fix this problem. We have 18,000 members across the country in GCA and I'm sure many of them use Comcast. If this is not resolved, GCA may have to use a different format that their members can use. You may lose them as a customer. Please let me know if this is a problem you have encountered other than here in Maryland.

Thank you

Please ask your ISP to whitelist our domain names and sending IP addresses: https://www.jotform.com/help/145-Whitelisting-JotMails-IP-Addresses 

If you have a Gmail account, you could use your Gmail SMTP settings for sending the notifications: https://www.jotform.com/help/244-How-to-Setup-SMTP-for-a-Form