Hello,
Our many clients recieving mails that is a failure message like the following.
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I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

:
Connected to 203.115.0.2 but connection died. (#4.4.2)
I'm not going to try again; this message has been in the queue too long.
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What we do from our side to avoid this error and send mails?
From where we get the blocked list, ie howmany are blocked our server and which are they?

Chirayil

There may not be much you can do from your end. The error message is basically telling you that the attempt is timing out before the other server answers. This could be caused by several things, including a misconfigured DNS on the other server.

Check on your end to make sure your own DNS is in good working order. DNSReport.com is good for this. Also make sure your firewall isn't blocking Port 53, as some ISPs require the ability to verify the sending machine before they accept email.