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Showing posts from April, 2015

The PTR DNS record, Email, SSL and You

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What is the relationship of PTR DNS record, email, and SSL ? This post will answer about that. Meanwhile, the background for this post are : I am unable to make my new SMTP server instance deliver mail to a certain company's mailboxes. The company uses Trend micro's reputation list to block unwanted sender. I have problems connecting to SMTP server using SSL with Android, and no problem using my Laptop and iPhone. I connect to the server using a load balancer IP address. The analysis First, to determine why the emails are not being delivered, I used the 'Delivery Status' display that available in the Cisco Ironport's Reports menu. It is quite useful when showing the reason why the email not being delivered. Using the url shown in the 550 rejection message, I found out that the IP address being used for the email server is listed as having 'Bad' reputation.  What is the meaning of DUL ? Quoting from Trend Micro website : Dynamic