"Sender address was invalid"????

Hi iliv4apl: I have encountered a similar error on my iPod Touch. Strangely enough it has been an SMTP issue as opposed to an incorrect address issue. If you are trying to send an email using a different internet service provider than Cox, it may be blocking outgoing mail. It is quite common for Internet Service Providers to block outgoing mail from "foreign" ISPs.

Hope this helps
Stedman

ISP is short for internet service provider.

If you have a wireless network at home, your iPhone is connected to the internet with Cox as the ISP when you are connected to your wireless network at home.

When your iPhone is connected to the internet via AT&T's cellular network, you are using AT&T as the ISP for your internet connection.

Most ISPs block the use of SMTP servers that are outside of the ISP's network or not provided by the ISP being used for your internet connection unless the SMTP server is authenticated. These restrictions are in place as part of an overall effort to prevent spam emanating from the ISP's domain.

A MobileMe account has an authenticated SMTP server, a Cox account does not.

Which ISP are you using for your internet connection when you are unable to send?

As I already provided, MobileMe has an authenticated SMTP server, and Cox does not.

I had the same problem - this post helped me fix the problem. I use Comcast.
In Settings, select "Mail, Contacts, Calendars....", then select your email account (Cox), select your outgoing mail server, then select Primary Server. At this screen you will see "user name" and "password". They may say optional in light gray. When I filled in the correct information, my out going mail started working.

You can also just add cwmx.com in "add server" in your outgoing mail settings. No user name or password needed. Then if you cannot send on cox it will try on the cwmx server. (at&t default server).
Just an FYI, you won't be able to send using wifi with at&t's server.

I'm having the same problem, but when I add the cwmx.com outgoing server, everything else on the screen is grayed out - I can't change server port or anything else (the port that is showing is 25). Any thoughts?

I got the same from my Cox account. The problem is the SMTP server. I and tech support got it working by setting the outgoing mail server SSL switch to ON. We also filled the password field with the same password used by the incoming mail server. Finally, set authentication to "Password" and use server port 587. Hope that fixes it for you.

Oddly enough, just scant weeks ago Cox emphatically told me SSL was NOT supported. Two observations: Cox is getting a LOT of these calls. And you think they would notify subscribers they are making changes to the server that will make iPhone/Touch mail erratic or just drop dead. They spam you about everything else.

BBFtL - thank you, this solved this issue for me