comcast.net not a valid (.net is not a valid site address on certain legitiment business sites)

This has happened to me a few times now.  Today I was attempting to file a reimbursement claim with Cigna Insurance and when asked to enter my email address the site responded with "please enter a valid email address".  I ended up using my business email which ends with ".com" and it took that address.  Is there a ".com" version of my Comcast email I can use or is there a work around?  Thanks for your help.

[Edited: Personal Information]