There can be many reasons why email client on iPad won't work for sending. It would be good if you can replicate the problem on a PC, and then use Outlook or Thunderbird to get the exact VM error code (VMxxx).
Another idea: Look up your external IP address using google search.
Go to spamhaus.org.
See if your IP address is in the SBL CSS block list. (or any other block list). Virgin use this list when permitting outgoing emails via email clients using their systems. (Not sure if this would apply to fasthost, but maybe?)
If YES, you have a spambot somewhere in your network and need to remove it - tell us and we'll advise a method. Then spamhaus will delist your address.
If NO, let us know and we'll try other ideas to diagnose.