Why people who have a .net email address do not get the email?

I've noticed that all the people who contact me, stating they did not receive an submission email all have email addresses ending in .net, whether it's comcast.net, att.net, verizon.net or sbcglobal.net. Is this something that can be fixed or should I discourage people who fill out our forms from using a .net email address?

Thank you

Hi, 

Unfortunately there's nothing we can do about that, if they don't receive an autoresponder it's because their mail service providers reject emails from us due to suspected spam or due to some other reason that we don't have any control over. 

Also, sometimes our emails end up in the spam/junk folders, so I would suggest that you advice your users to check their spam folder.

Thank you!

I appreciate your prompt response. Thank you.