The sender address was invalid

I turned off both Comcast outgoing smtp mail servers and turned on the AT@T smtp server. Now all is fine with outgoing email from both our iPhones. Hope this is a permanent fix.

If I try to edit my gmail setting, it won't let me get to name, password for SMTP. Will I have to delete the gmail account and set it up again?

Thank you, thank you, thank you. I've been trying to solve this problem for the last 7 days with the help of Apple and my service provider, but neither of them had a clue. Thanks to you, now I can get back to business (and get some sleep).

Thank you so much! I have been having this problem for the past month and couldn't find anything on the support site!
YOu are awesome

I found that by changing the out going mail port to 25 it fixed the problem,

I had to change the outgoing server to Port 25 and had to turn off SSL to get my iPod Touch to use Comcast's email server via my home network. Now all seems smooth (fingers crossed).

I'm having the same problem but i can't change any of the smtp settings, there all grayed out so I can't touch or do anything with them. I'm not sure what else i can do.

Just wanted to say that for me, changing the port to 25 worked as well and SSL is on not off.
Thanks for your help. I also set up a secondary SMTP just in case but I haven't had to use since the port change.

My iPhone 3G was fine up until today. I've sent emails today, and after like 10 mins after sending my last emails i was unable to send anymore emails.. receiving the message 'the sender address was invalid'. i'm able to receive but not send... i have a gmail account.. So after reading all this the only thing that worked for me was turning off the primary server and turning ON my Rogers SMTP server.... i hope this works and lasts

I have a Ipod Touch 2G, which was fine for the last month until today. Getting the "sender address was invalid error". I am not in Canada, and this is on Wi-Fi (obviously).

My only account is with gmail. when I compose a new message now, it goes right to the outbox and keeps trying to send and always fails.

I have not changed any settings. This happening to anyone else?

OMG! I am having the exact same problem. It has to be Google tweaking something.

I must confess. I am not having the problem with an iPhone, it is with an iPod Touch with the 2.0 software update.

Giles Savard1,

This error message means that the SMTP server you are using is rejecting the message. Essentially the SMTP server won't accept email to relay on when it is coming from that address, on the network it is currently connecting to the server through.

This can be for several reasons, all related to measures ISPs have taken to try and prevent spammers.

For example, at home my personal ISP does not require authentication. I can send all day without telling them who I am when I am at home. They already know who I am because I am coming within their network, and the accept email on Port 25. If I am away from home I have to use Port 465, and username and password. Some ISPs won't let you relay when you are off their network at all. For those you have to use an alternative SMTP server, such as cwmx.com for AT&T customers.

You may also get this message if you are connected to a network which blocks the port you are using to send. Port 25 is blocked on a lot of networks. Some WiFi networks even block Port 465 and 587, which are the most common for alternate ports for SMTP.

Spammers ruined open relays that didn't put up these kind of filters, by abusing them to send out spam.

Hope this helps,

Nathan C.

I've been having this error since yesterday, on my iPhone 3G (Rogers network). Solved it thanks to the various tips provided here.
*I just changed my smtp.gmail.com port from 465 to 25 and turned SSL OFF*.

For those who are still having problems, here is my configuration:
Primary Server: Host name: smtp.gmail.com
Username: myusername@gmail.com
Password: mygmailpassword
Use SSL: off
Authentication: Password
Server Port: 25

Hope this helps.

Well, here's my problem: I can't change the server port or any of the advanced settings on the Ipod. They are all grayed out.

The primary server was setup automatically when I first set up the gmail on the Ipod. Should I delete it and try to set in manually?

Currently my port is 587

Message was edited by: MadisonMini

MadisonMini,

GMail uses 587 which is one of the least likely to be filtered. If it won't send when you are on a WiFi network, try on Cellular Data instead.

Hope this helps,

Nathan C.