unable to send email on ios device

Having difficulty sending emails from my cox account when overseas in Europe. When trying to send an email from my device, I immediately receive the message: "the sender address "xxx@cox.net" was rejected by the server. I had a read over Cox's article on IMAP server settings (https://www.cox.com/residential/support/imap-server-settings.html) but confused if it has something to do with my security encryption version or if it's because I am overseas.