Can a dns be used to make a personal email account?
 

I have a hostname with dyndns and I was wondering if there where
a way to make a mail server that works for all my user accounts with
the hostname that dyndns gives for free.

In order to receive mail on your server, you need to create MX records.
This can only be done if you have a DynDNS Pro, not the free service.
http://www.dyndns.com/services/dns/dyndns/
Most SMTP servers will reject mail sent from a dynamic IP, so sending mail will not work, unless you use a smarthost, like the SMTP from your provider.
Another point, is port 25 open, does your ISP allow you to run a mailserver on your dynamic IP?
You will have to let your server run 24/7.
You need to have a backup MX to receive your mail in case your server or the connection goes down.

Kind regards

My server runs 24/7
 

Can I ask you something else. Is there a way to
make my own dns using linux? Or do I have to first
purchase a certified domain name?

You have to buy a domain name. If you want a real '.com' etc. you can use other providers like no-ip.com to get free domains like myhouse.no-ip.com if you are happy with that uglier type. You can certainly run your own dns servers if you wish, but it's normally pretty pointless, with minimal benefit. First thing though is to get your dns server pointed at to answer questions, and that's done by your domain of choice having its NS record set to point to your name server, and you can't control that but yourself.