Ok it has been a while since my last update, and I dont think it is because I am running out of stuff to talk about. Today lets just do a simple grep trick. Lets grep some stuff out of a maillog 

grep -i rejected /var/log/maillog

 that should give you about 2000 or so returns. But what if you are looking only for rejected messages from yahoo.com? Lets string some grep commands together shall we. 

 grep -r rejected /var/log/maillog | grep -r yahoo.com 

Now we are starting to narrow it down a little bit, we see only messages from yahoo.com, lets see if your email address is actually being rejected now 

grep -r rejected /var/log/maillog | grep -r yahoo.com | grep - r irocksbigtime  

Now you  you should see just your mesages 

 19:24:25 vsmtpin3 postfix/smtpd[28336]: NOQUEUE: reject: RCPT from unknown[192.168.1.101]: 504 5.5.2 <GNTDJLCVL>: Helo command rejected: need fully-qualified hostname; from=<irocksbigtime@yahoo.com> to=<XXX@XXXXXX-XXXXXXX.XXO> proto=ESMTP helo=<GNTDJLCVL>