hmm none that not much help im guessing by a client u mean an email server that u can send and recive email trough thunderbird wont do that it just downloads emails to ur computer from the email server
here is an email server software it's free but it has limatations
Free Edition | SmarterMail 4.x | SmarterTools Inc.
next u need a firewall if u dont have one ur router then u need a software one make sure all the ports are closed apart from ports 80 25 21 and 110 these ports are for web ftp smtp and pop server thay are the only ports i recomend u open if u do not open these then nothing will work lol.
how ever saying all that i agree with these guys just go to a webhosting company much easier
also on the mail server one u may not be able to send or recive email depending on ur isp as a lot of isp's are starting to block that port
u will also need to check that ur ip is static others wise every time ur internet disconects u are going to get a differnt ip and the domain u brought will no longer be pointing at u
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Look what my computer did to me:

shouldn't it be the other way around..
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Here to help others with computer problems and learn new things at the same time. No one knows everything, if they did, life would be pointless.
not bad for a 512KB conection which is the fastest i can get!!!!!