[OT] email from self?

["Malcolm Surgenor" <malcolm@xxxxxxxxxxxx>]

I rarely see spam emails nowadays thanks to some decent filtering but today
i've noticed a few coming through that haven't been filtered out.  I can
see why not but can't figure out how it's done.  The emails all appear in
my inbox with the 'From' set to my own email address - i.e. my actual
domain name email address and not any alias.  Obviuosly i haven't sent them
but is it possible from someone else to send out emails in my name?  Should
I be worried or just work out a way to filter them?

TIA

Malcolm