Unable to send mail through 3G / cellular newtork - only over wi-fi??

I have exactly the same problem, (I have 3 Gs iphone), have tried solutions suggested on this forum but to no avail.

This solution worked for me:

It was very simple at last. Keep your WIFI-settings for outgoing mail, just add authentification for outgoing mail, and enter your login and password (same as for incoming mail).

SETTINGS > MAIL, CONTACTS, CALENDAR > "Your account" > SCROLL DOWN TO "SMTP" > PRIMARY SERVER > USERNAME -enter your login / PASSWORD -enter your password. AUTHENTIFICATION > "password"

Good luck

I seem to have cracked it. My mail login is in the format zen11111 (not my real user name of course) plus pass word for the pop3 server. When using email at home the smtp server requires, as usual, no user name and password. Following advice from here, I was just putting my pop3 login name and password in the smtp server. However, it seems my ISP's smtp server requires @zen.co.uk to be added to the login name. So now I can send emails without the need for wi-fi

This worked for me. Thanks!!

for the UserID, I entered my email address without the @comcast.net

I just fixed this issue on my Iphone 3GS after multiple hours over the last few days. It was very frustrating. After my second call to tech support to my broadband service provider he made a suggestion a half hour in that seemed remote but solved the problem.

When you enter in the outgoing Mail Server information you may need to enter your entire email address into the User Name field.

My broadband provider is Braodstripe in Seattle, WA and is flakey on service outages and had no real web site help documents. Over the phone the tech ran me through the settings their telephony tech guy used on his Iphone and I will repeat them here for people on Broadstripe and for those looking for some type of solution. PS I did not have to do the Name Field change on my Iphone 3g.

Account Information:

Name: Just the name that will show up and has no influence.
Address: email address
Description: Filled in by phone but you may change if you want - no influece.

Select POP

Incoming Mail Server:

Host Name: mail.cablespeed.com (use yous ISP of course if not on Broadstripe service)
User Name: name
Password: password

Outgoing Mail Server
Host Name: mail.cablespeed.com
User Name: Leave blank
Password: Leave blank

Click on save and if your do no use SSL with your mail servers click yes to setting it up without ssl. You will have to click twice and each time takes 2 to 3 minutes on Broadstripe.

Now touch the Outgoing Mail Server button (SMTP) with mail.cablespeed.com next to it.

Select Primary Server mail.cablespeed.com and NOW enter your Outgoing mail server information

Host Name: mail.cablespeed.com
User Name: name@cablespeed.com (not just name)
Password: password


Click back using the SMTP back key at top left then hit the home button and your are good to go.


If you are having trouble sending from your SMTP mail servers while you are on your Iphone using cellular, on a laptop using a wifi hotspot (but not your home wifi through your broadband provider), using your Iphone as a broadband router/wifi hotspot, etc try changing your Outgoing Mail Server User Name to your entire email address.

For those wanting to know why this was happening:

I could not figure out what was going on over the past week until my broadband service went down and I needed to use my Iphone to get internet access. That is when I noticed that Outlook was giving me sending errors but no receiving errors - just like my Iphone which could recieve email through the POP server no problem. HTTP access was fine. Just could not send emails. Luckily Outlook has a much better error reporting capability than the Iphone so I was able to read the real reason on the screen even though it did not give me the immediate solution shown above.

With the 'My outgoing server (SMTP) requires authentication" box unchecked I was getting a 550 5.7.1 relaying denied error during sending. With the box checked it was looping the enter password pop-up box. My SMTP server does not require authentication when you are connecting through the IP address associated with your high speed internet service (if you are using their SMTP server) but does when connecting though an unknown IP address such as a wifi hotspot or your Iphone.

And the key to getting my particuliar ISP's SMTP server to recognize me correctly was to change my name to my entire email address (name@domain.com) versus just name.

Of course when I made this change in OUtlook while useing the Iphone tethered I was able to send from my home computer as well.

I hope this helps some of those having trouble with sending from their home computers SMTP server.

One more suggestion given out is this once you recieve an email from a POP server on some ISP's it will correctly authenticate the SMTP server for that IP address you used to access the POP. So try to recieve from the POP server as well if you have not done so already.

Add another SMTP server (there can be more than one). Set it to cwmx.com, no user id or password. This is AT&T's internal network SMTP server. So if you are not connected to WiFi it will try the WiFi first, then when that fails it will use cwmx.com. There will be a delay in sending, but the message should eventually go.

I'm really curious now as to what the problem was after reading all these posts. I had the same issues on my 3G before the 3.0 update and after downloading it. I could not send any emails over 3G network, I had to be on a WIFI network, otherwise I'd get the familiar "address invalid" dialogue window.

I called AT&T and asked them about a mobile 3G SMTP server or something as my Road Runner ISP was of no help, but this very nice lady said no, I simply gave her my iPhone ID, she ran a test, told me to restart the phone, turn off the WIFI as I was at home, and try a test email, and it worked?

What did she do that suddenly enables an email over the 3G network, I'm curious?

I'm curious also. I have a suspicion, which I'll get to in a moment. First, SMTP (outgoing mail) servers are completely separate from the incoming mail servers at your ISP. They may or may not have the same URL, but is is quite common for them to be different (outgoing.myisp.com vs incoming.myisp.com). And there's nothing in the Internet protocol to prevent you from using any SMTP server you want when sending email. You could even have your own on your computer (which is what spammers do, except they co-opt your computer with a virus and secretly install an SMTP server on it, then send their spam through it).

To prevent spammers from using the ISP's SMTP servers there are two strategies: The first is to allow only computers on the ISP's network to use its servers. BellSouth and I think RoadRunner do this. You don't need to enter your user ID and password for sending, because the server knows who you are from your IP address. But this means you cannot use your ISP's servers if you are not at home.

The other strategy is to require you to enter a user ID and password when setting up the SMTP server on your phone. The ISP then knows who you are from your credentials, and will allow you to use the server whether you are on their network or not. Verizon DSL and FIOS work this way. This is actually less secure for spam prevention, because it's fairly easy to guess many people's passwords, and your user ID is very easy; it's your email address.

If your ISP uses the first method you cannot send over WiFi using their server if you are not on your home network. So AT&T (and all other carriers) have a special SMTP server that works like the 1st method, but on the carrier's network. For AT&T the SMTP server address is cwmx.com (Cingular Wireless Mail eXchange; remember, AT&T is Cingular rebranded).

If your ISP uses the first method and you are on some other WiFi network you can't normally send over WiFi, which is why you sometimes have to turn off WiFi to send. But there are workarounds; many WiFi providers intercept the sending SMTP server address and redirect it to their own SMTP server, so you don't notice. The other option is to subscribe to an open SMTP service. This is usually not free, but is not expensive either.

As to what happened to you, I've noticed that the number of messages reporting problems sending email has dropped dramatically recently. I suspect that Apple or AT&T can now remotely add cwmx.com to your server list in your phone.