Postfix not delivering to inbox

So i have 5 vps with ubuntu LAMP 10.4 I use postfix as MTA. all worked fine but yesterday my only 1 vps was delivering. the rest wont send. it says its sent but when i check my gmail its not there. not in spam, not in inbox. the ip is not blacklisted. i flushed postfix que. any ideas why the email is not delivered
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Are there any errors in your mail log (in the /var/log/ directory)?

 

re

I cant find the postfix log in /var/log There is no mail.log or anything like that. WHere is it?

 

Are you sure you have a mail server installed and that it is running?

What's the output of

Code:

ls -la /var/log/

?