linux postfix config and hostname FQDN

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http://stackoverflow.com – I'm trying to setup a mail server with postfix and dovecot using the tutorial from https://library.linode.com/email/postfix/postfix2.9.6-dovecot2.0.19-mysq... I followed every steps and also openned every mail port in the firewall but when i try to setup my email client to connect with IMAP or POP3 it just can't etablish the connection. It appears i can send email to my domain using my private emailbox. Anyway my log /var/log/mail.log is empty. I guess it has something to do with setting up a hostname (FQDN) and the postfix config. But i'm a bit confused about hostname and F (HowTos)