mystified by mailto address

[Ben Elliston]

>>>>> "Simon" == Simon Fowler <simon> writes:

  Simon> It can be a problem at times, because the receiving mta has to
  Simon> understand the format; sendmail does, and postfix does (if
  Simon> configured correctly), but I'm not sure about others . . .

Does the + syntax have a specific name to identify it?  I would like
to configure my Postfix to be able to use it, but that would require
knowing what to look for!

Thanks, Ben