The mail sent from the server does not reach to Yahoo users. Whereas sometimes, it appears in spam folder of gmail account.

How do I correct this problem?

  • 3
    you should post the email from the gmail spam folder, including headers, excluding personal data, here. also, this probably belongs to superuser.com.
    – ax.
    Commented Oct 8, 2009 at 6:52
  • I have figured out that one problem is related to "from" headers i.e. c18-ss-1-lb.cnet.com and it resolves to nslookup of com.com How do I correct this now?
    – shantanuo
    Commented Oct 8, 2009 at 7:49
  • I've updated my answer with your additional information. That IP address block has reputation problems...
    – Jim Lewis
    Commented Oct 8, 2009 at 8:14

6 Answers 6


Basically, make sure that you are not doing the stuff that may trigger spamfilters, like:

  • Including URLs
  • Incorrect/untypical headers (for instance, include html-version but not plain-version)
  • Sending e-mails to several users
  • Include content that triggers spamfilters


I suggest that you find a spamfilter expert on how to avoid this, so that you can also test your e-mails. The spamfilter expert can evaluate your mails and tell you where to spend your time on improving your software.

Also, if possible, create some kind of mechanism that gives you an automated success ratio, so that if the spamfilters change in a way that makes your software work less well, you will be notified immediately.


Maybe your outgoing SMTP server has been abused by spammers in the past, and has ended up on somebody's public or private blacklist. Here are a couple of sites where you can check the reputation of your mail host by IP address:

Sendmail IP reputation tool

Spamhaus SBL list

Edit: Your SMTP host resolves to IP address, which has a poor (spammy) reputation at sendmail.com (see above link). (It came up clean at Spamhaus).

This is quite likely to be related to your deliverability problems. Try an address at Hotmail -- I bet they bounce it, too. I'm in the same boat with my own ISP -- they changed IP allocations, and from that point on Hotmail started rejecting all my email. My ISP, like yours, came up clean on Spamhaus, but suspicious according to Sendmail.

  • Does it mean that it is ISP issue and I can not do anything about it?
    – shantanuo
    Commented Oct 8, 2009 at 9:11
  • @shantanuo: Well, there always the option of setting up an SMTP server in a "better neighborhood" and routing your outgoing mail through it. You're unlikely to convince an operation the size of Yahoo, Gmail, or Hotmail to poke a hole in their filters for you. (If you're a paying customer of cnet.com, they really ought to be working this issue on your behalf!)
    – Jim Lewis
    Commented Oct 8, 2009 at 9:28
  • You may be on a blacklisted domain/IP/range.

It really depends on the algorithms that Yahoo and Gmail use to identify spam. Something about the emails you're sending seem "spammy" to their filters.

You'll want to check a few things:

  1. Make sure that your reply-to address is from the same domain as your SMTP server
  2. Don't send from a domain that sends a lot of spam - it may be blacklisted
  3. The text of your email should avoid sounding spammy. If you're promising anything "cheap" and/or "completely legal," then you're going to set off filters.

Lastly, and I hope this goes without saying... Don't send spam. :)

  • Avoid behaviour that let think you're "namespace mining" their servers (sending a lot of emails to a lot of unknown users, for example).
  • Make sure that your SMTP server is actually listening and not just bouncing emails/DSNs. I hate that. ISPs hate that too and will blacklist you for that.

Cam's and Lars's answers are very helpful too.


My IP is blacklisted in the CBL list.


It says: "This is the maazben spamBOT " What does it mean and how should I correct this problem?

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