I have had an issue with the email setting on my iphone 4 for a month now and I JUST figured it out. So, I'm writing here to keep a record for myself and to help anyone else who has this problem currently or in the future.
So, I've had my phone for about a year and last month my home email got hacked and started sending those stupid spam messages to my address book disguised as me. Hate that.
I went into my home email and changed the password, then went into my iphone and changed the password.
Suddenly, my phone would receive emails but would give me an error message when I tried to reply or compose a new message. I spent so many hours trying to figure this out I was about to throw my phone out the window! I was going in circles!
So, the easy fix for some people is to make sure you change your password in both the "incoming" and the "outgoing" settings of your iphone. It's easy to overlook the outgoing option.
This did not work for me, here is what did work:
* Go into settings and choose "Mail, Contacts, Calendars"
* Find your email provider under "Accounts"
* Scroll to the bottom of the screen and hit the red button "Delete Account"
* Now, here is the secret! Reset/Reboot your phone by pressing the "Power" (on the top edge) and the "Home" (the round one on the front) at the same time until the apple appears on the screen.
* Let it reboot for a few minutes and when it comes back on, go back into settings/mail/accounts just like before and this time select "Add Account" and reenter your email information.
* I also saw a tip to not use any special characters, just numbers and letters.
I hope this works for you!