Outgoing mail delivered in spam folder by using sendmail@Linux?

Question

I have configured a mail server by using a valid domain having reverse and farword entries in the DNS of my ISP, but all of the outgoing mails from my server are delivered in spam folder. All this is happens with gmail, hotmail and yahoo please advise

Answer 1

First I would examine the headers on the e-mails. Make sure the info in the headers give the correct information as to where they came from (your mail server name, IP address, etc.  Email is considered SPAM if the information in the headers do not have the correct information.

Next, I would verify your reverse DNS lookup is correct. You can do this by simply going to any computer connected to the internet and running the command line, NSLOOKUP.  Type in your mail server IP address. It should return the proper name, like "mail.yourdomain.com."  Then reverse it, type in the mail server name, and it should return the proper IP address. If it does not, then your DNS is not setup properly.

Verify your virtual SMTP server is configured properly with your mail domain (mail.mydomainname.com) This is a very common thing overlooked by people setting up Microsoft Exchange for the first time.

In addition to these steps, find out if the IP address your ISP has assigned to you may be on a blacklist, like SORBS. If this IP address has been used previously by a known spammer, then you will have these problems. It's easier to get a new IP address from your ISP than to spend a lot of time getting it off of a blacklist.