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I received a lot of complaints from my users, they say that they can't find the activation email. I didn't do any blast emails or send spam emails. But I do send over 1000 emails daily, that's because of the signup. That means, in my registration process, I will send an activation email to the user to activate their account, and I think this is quite a standard method.

I tested my company email and gmail accounts, it works fine, only hotmail and yahoo emails, they just could not receive any emails from our website, not even in the junk/spam box.

Can anyone help me on this?

My server: Windows Server 2003, IIS6

Programming language & database: php and mysql

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Your email server may be on a blacklist, might not have a proper reverse lookup record, if you're on DSL it could look bad if it's too close to dynamic ranges (even if you have a static IP on "business class DSL") and a number of other things. Check the free tools on to see if any of those apply to you. You may want to consider creating an SPF record for your domain as well. That can count in your favor in a Spam Confidence Level weighting algorithm. However, nothing can help you if you're on a blacklist. Get that checked out first.

EDIT: In addition:

  1. Check a more thorough DNSBL like
  2. Read this article about spam, newsletter emails and major email providers:
  3. Take it up with the postmaster system at the problematic domains. I.e.
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I checked. My domain is not on the blacklist. What should I do next??? – mysqllearner Nov 24 '09 at 4:47
As @nonapetide said, check the tools on – mrdenny Nov 24 '09 at 5:09

I recommend signing up for a free account on They have some very useful tools for diagnosing why your mails might be being rejected.

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