Hey ho! I've been invited to a party  

The invite came via email and yes, my email address sits there clearly along with the other 50 or so recipients that it's been cc'd to. A charming couple according to the wording of the invite; I know of the venue and it's not that far away; the date is in early July and would be feasible and if the weather holds it should be loads of fun.
The only problem is ...
I have never heard of these people before!  
 
  
  I don't recognise the sender or any single one of the recipients  
 
 
They all appear to be bona fide UK email addresses, some company addresses, others various...  

HTF can that happen?  

Should I go along? On a wing and a prayer ...  

 ...