This sounds like a problem with the outbound mail settings on your device. I don't have an iPhone, but I do have an iPad that sends and receives mail on the Cox network. My outbound server settings are as follows:
Go to your outbound server settings in your Cox email account and change the following settings if necessary:
1) SMPT host name should be smtp.cox.net
2) User name should be the part of your email address left of the @
3) Password should be the same as your inbound
3) SSL should be ON
4) Authentication should be set to Password
5) Server port should be 587
It's a little confusing because Cox is saying that SSL doesn't work anymore but Apple doesn't have a choice for TLS. From what I've read, Apple uses TLS when SSL is turned on and the port is set to a valid TLS port number.
SSL should be ON
The POP server immediately rejects my logon if I opt SSL.
