Good morning The Rock and welcome back to CH
#1... Make sure the EU main account is set as default email account
#2... Change the receive time to 1 or 2 min
#3... Use outlook detect and repair (this can fix some issues in outlook)
#4... try sending an email from another PC to the trouble user's PC and then reply back does it work?
#5... Disable outlook add-ons some add-ons can be a royal pain
Do you get any errors on send and receive when you push the button?
Hope this helps please let us know how you make out. Mike