Postfix smtp server works from localhost but not from afar

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http://serverfault.com – I'm trying to set up a smtp server on my domain (wixencafe.net), and i'm using postfix for that. First thing is, postfix delivers emails coming from outside, that is, if i send an email from gmail.com to wixencafe.net, i get the email in my Mailbox/ Second thing is, if i send an email from wixencafe.net (from the server cli via mutt -f Maildir/) to gmail.com, i get it too, so i guess that means everything works fine. Now, my problem is, if I try to send emails from my desktop (which is not on the same network than my server), it just doesn't work. From thunderbird, i get a delivery error, a (HowTos)