Vodacom smtp problems

Brainteaser here,please advise...

Got a vodacom 3g modem giving me internet & email connection to my pc.
I have got outlook 2010.
No problems receiving email but get the following error sending:
"Server error 554 5.7.1"
"Helo command rejected: Please setup a hostname (FQDN)"

I have used smtp.vodacom.co.za and smtp.vodamail.co.za as my outgoing servers.
Have googled that error but cant find a solution

Any ideas?

many thanks