Ok so i have setup my mail server using postfix.

My understanding is that this controls the sending and receiving of mail am i correct?
mail is sent threw port 25 on SMTP protocol?
mail is received threw port 25 also?

My configuration file is now this is a problem because anyone can send email threw my server and i do not want that. Because do not want to be a relay but i do want to handle my own emails going in and out.

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no
append_dot_mydomain = no
alias_maps = hash:/etc/aliases
myorigin = $mydomain
mydestination = mymailserver.org, localhost.localdomain, localhost.localdomain, localhost
relayhost = mail.esat.net
mailbox_command = /usr/bin/procmail
mailbox_size_limit = 0
recipient_delimiter = +
home_mailbox = Maildir/

So i thought i would block the port forwarding to port 25 on my router but this did not help because I stopped receiving emails. Does this sound correct?

I have Dovocot setup with imaps to check my emails.

Thank you

there's no mynetworks definition, which is probably where your problem is coming from. mynetworks defines what sources can use you as a relay, ie. who can give it mail not destined for the server itself, but some other domain (i.e. who you are sending mail to at hotmail etc..) so add that and you'll see a big difference, e.g. mynetworks=192.168.1.0/24 for a fairly standard local subnet.

and mail isn't sent and recieved on port 25 the way you suggest. smtp servers pass mail to other smtp servers, which all listen on port 25. so if someone sends YOU mail, they connect to YOUR port 25. if you send someone else mail, you connect to THEIR port 25, so it's exactly the same process, but from the other side, yeah?