The problem is that by default infopop set their systems to refuse anything that has a - or a . before the @. It is the same with opentopic, and I guess with ubb.
The majority of email systems recognise these type of addresses, but some big boys like the BBC do not - their email system will bounce these types as being invalid.
I am not sure if it complies with the guidelines for email addresses - but certainly the majority of servers will allow you to issue such email addresses, so I guess that threads & opentopic should allow them.
Interestingly I see that this thread does not have a subject in replies - did threads strip the subject automatically?
at the moment - but expanding all the time....) 
