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I have a CentOS installation with bind/postfix/dovecot. After I installed it I tested and I could send emails to any direction without problems. After some time (maybe a month or so) when I tried to send an email I noticed that it wasn't delivered to destination. When I checked the logs I found something like this:

    postfix/smtp ... host[] refused to talk to me: 451 too many connection attempts
    postfix/smtp[26671]: 2EFC411083A7: to=<email_here>, relay=none, delay=120, delays=0.02/0.01/120/0, dsn=4.4.1, status=deferred (connect to[]: Connection timed out)

It does get sent to some small mail services but not to major like gmail yahoo or hotmail. The issue is the same above. I googled a lot for this error but found nothing that would solve this.

It does happen on CentOS 5.5, postfix 2.3.3

Does anyone know how to fix it?

UPDATE: Everybody tries to tell me that I send too many emails. This is not the case. I wasn't sending any email from this server. I just installed it, configured, tested, and forgot about it. Just used to develop web applications on it. And no, there isn't any web application on it through which somebody could send tons of emails. And I checked the logs and there aren't any email sent from this server. So the problem is not that I or somebody else used this server to spam or to send tons of email.

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up vote 1 down vote accepted

There are various things you can try, from the top of my head:

  • Install & configure Domainkeys
  • Ensure there is valid reverse DNS for your server
  • Ensure there is a valid MX & SPF record for your server
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I had Domainkeys installed when I noticed the problem. I tried to remove them to see if the problem persist. I have SPF and MX records. – JohnZ Feb 17 '11 at 18:24

If you send large amounts of e-mail to gmail, hotmail, yahoo and other large providers, they will throttle you if you don't play nice and/or if they don't know you.

Google gives advice here:

Yahoo! here:;_ylt=AhmGh0eprkWxD1JL6AX_CBUIJHdG

Hotmail here:

Also with you can look at which more and more providers are implementing.

And here:

Those links should provide you with a lot of good information on how to handle bulk e-mail. If you do not follow those guidelines you will get blacklisted, throttled and get bad reputation.

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I wasn't sending ANY emails. – JohnZ Feb 17 '11 at 18:23
Someone or something from your IP address is hammering Google. You will not necessarily be able to see that in the logfiles, if a script or something like it is hammering google bypassing your MTA. – Frands Hansen Feb 17 '11 at 19:00

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