the email problem may be related to your host and not the people recieving. Ping your domain name at the command prompt,..
for example if your email is @worldOnline.co.uk you would c:\ ping mail.worldOnline.co.uk
this should give you an ip number
go to
www.mail-abuse.org and see if they are listed. if so then poeple who's isp blocks your can't get your email.
example of isp blocking sites due to spam:
Roadrunner (rr.com) is blocking according to list and will soon block yahoo Groups and clubs.
Anybody running a big game i would suggest switching to a web/ftp site to publish and recieve turns, even if just as a backup.
thanks to spammers your email is no longer reliable, so make sure you have a work around.