Setting up Verizon e-mail account on Iphone

I have set up my Verizon e-mail account on my Iphone (I was disappointed to find out that Verizon doesn’t have an Iphone app as does Comcast), and I can receive mail, but when I attempt to send mail, I get the message, “the sender address was invalid”.  I tried to contact Verizon technical support, but they said they do not answer questions about the use of Verizon e-mail on the Iphone.   I had the same problem when I was setting up my Comcast e-mail account on my Iphone, and I remember that I had to change something in a setting on my Comcast e-mail account.   I’m sure this is also a setting change.  Can someone please provide assistance?   I do not want to use yahoo or gmail or anything else like that, and I am sure some Verizon Iphone user out there somewhere has this figured out.  Thanks.