Hello, my name is Dan.
I will do my best to help you, the only stupid question is the unasked one.
In prodder of things to try.
Reset the iPhone.
To reset the iPhone press and hold both the Sleep/Wake and Home buttons down until the Apple appears, ignore all other screens, then let go.
This does a system reset much like a restart of your computer does.
If that fails, quit the Mail app, do this by double tapping the Home button so you get a row of apps along the bottom of the screen.
Hold your finger on one until it wiggles and a red - appears.
Tap the minus to quit the app, it will not delete it.
If that does not bear fruit then delete the SMTP info and reenter it.
If that fails then delete the account from the iPhone and recreate it.
Use the same info on your computer.
If that all fails then please let me know.