the output of postconf -n
would go a long way in determing what might be wrong with your configuration..
Also verify mydestination, mydomain, myhostname, mynetworks
are all set correctly in your postfix configuraton. if these are incorrect you can cause the server to allow relaying or cause other servers to deny mail from you.
also make sure the hostname on your mailserver is set to the FQDN that is registerd to be your mail server, and set in the myhostname variable, and that rDNS has been configured for your mail server by your DNS hosting provider.
If a mailserver you are attempting to send mail to does a rDNS lookup on your mail server and doesn't get a valid response it may deny accepting mail from you.
If a mailserver you are attempting to send mail to does a hostname check against the name your server provide during HELO and doesn't get a response that matches the Registered name of your server it may deny accepting mail from you. as well as submit your server to a blacklist.
Setting your Hostname
As for the Queue, the mail in the queue will time out eventually and be removed by postfix automatically, this is set at 5 days by default. This 5 Day time limit is INTENTIONAL, and is part of the design of a proper mail server so you probably don't want to change it.. maximal_queue_lifetime (default: 5d)