Email says sent but wont actually deliver-please help iPhone

This is so aggravating. Sorry in advance for the long story:
My work email server has always synced just fine to my iPhone for the past 4 months. Earlier this month my work email stopped sending - it says its sent and shows up in the sent folder, but it doesnt actually get delivered to the recipient.
I have tried everything I can find. Heres a list:
Updated iPhone software.Updated iTunes software.Synced using iTunes. Then synced manually onto the Phone.Got the Apple store to patch my iPhone with something calledDFU? Worked for an hour and then stopped.Turned extra SMTP servers on.Tried different SMTP servers as primary outgoing server.Wiped entire iPhone about 100 times.Turned WiFi off. Then tried using only WiFi.Tweaked every single configuration - turned off SSL, changed the port number, etc. Ive now had two IT departments not be able to figure this out.Tried syncing my work email to other iPhones both in my firm and at the Apple store. Both worked fine.Finally, I swapped my iPhone for a new one (was under warranty and it seemed to be a handset problem). Worked perfect - until today. Then it stopped again. Tried wiping the phone twice. Nothing.
It seems sometimes that being in my apartment (which is cement) is where the problem will start, except then it wont work ANYWHERE after. Plus I cant tell for sure where it happened the first time - whether in my apartment or outside.
HELP! This is so annoying. Im so tempted to sell my stupid phone and go back to Blackberry but Im scared that wont work either.
iPhone 4 iPhone OS 3.1.3