iPhone outgoing mail is rejected by server. What's that mean??

[CountessVonKnackerstein]

It's with O2. All my gmail, hotmail and yahoo accounts work, but not this new one which is using OUTLOOK and my business email account....
I am just not sure what setting has gone wrong!

Are you receiving mail on that account correctly?

Confirm your server & account details with your IT dept.

Receiving totally fine!
It's just sending there is a problem with. Odd, innit!

Mine was playing up today as well.

I have the same problem when using 3G but not when using wifi. I have no idea why one works and the other doesn't.

Actually....it does send but not straight away, sorry forgot to add that. Takes about 30-40 mins to send.
Doesn't seem to matter if I'm on wifi or not!