Exchange error sending mail

Hello:

I'm using Exchange 2010 Queue Viewer tool and sometimes appear mails that cannot be delivered with error "451 4.4.0 Primary target IP address responded with: 421 4.2.1 Unable to connect. Attempted failover to alternate host, but that did not succeed. Either there are no alternate host, or delivery failed to all alternate host"
The recipient email address is correct and the server is working ok with other recipients.

Thanks.
danigomeAsked:
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OsmozeConnect With a Mentor Commented:
so that's the problem i think , you should contact them to get the certitude that youre really blocket atheire  side .
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farazhkhanCommented:
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farazhkhanCommented:
Hi,

This will help you too with ease: http://www.networkadminsecrets.com/2010/04/421-and-451-exchange-2007-errors.html

Regards,
Faraz H. Khan
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danigomeAuthor Commented:
I've created a new Send Connector using guide at http://www.networkadminsecrets.com, but the emails stand at the queue and retry command doesn't work. The error is the same.
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farazhkhanCommented:
Hi,

Check event viewer and see what it says about this specifics!

Regards,
Faraz H. Khan
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OsmozeCommented:
did you use a smart host to forward email ?. (antispam gateway ? mail rely ?)
do you have any firewall in place ? could you check in its log if he blocks smtp traffic to some domaines ? can you check use external DNS mx records in the send connector propreties and try ?
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danigomeAuthor Commented:
I don't use a smart host to forward email and the domains that fail was woring before.
In the new send connector I've checked "Use external DNS Lookup..." but doesn't work.
I had a Spam problem with my public IP address, but I could to resolve it and the IP doesn't appear in any black list.
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danigomeAuthor Commented:
I've checked event viewer and I couldn't find any error about this issue.
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OsmozeCommented:
try
telnet IPofFaildDomain 25

to see if you can reach the SMTP port on this domain and the mail flow in not blocked .

(telnet is not default installed on 2K8R2 you have to install telnet client from server manager first )
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danigomeAuthor Commented:
Sorry but I don't know the IP of the domain. Is an email address from ipspain.com domain.
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OsmozeCommented:
you can get the MX IP addr for a domain by

nslookup q=mx www.domain.com

try doing this from exchange server if you get a black empty screen that the port is open and mail flow can reach the destination
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danigomeAuthor Commented:
Ok. I've used telnet to www.ipspain.com IP at port 25 (got it using nslookup, as you said), but I get "connection error" message.
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OsmozeCommented:
if telnet @IP 25   failed (it's important to specify the 25 port in the command ) that means there's somthing blocking the smtp traffic to this @IP or ,the destination donot accept smtp trafic anymore from your @IP .
it's not on Exchange server you have to investigate somewhere else .

for example :
(l.mx.mail.yahoo.com  is one of yahoo's mail servers )
i do telnet l.mx.mail.yahoo.com 25      (try it  from your exchange server not from other machines )
i got the black screen with the greeting mssage .
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danigomeAuthor Commented:
Is possible that my IP is not allowed in ipspain.com domain? How can I detect and to solve this issue?
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OsmozeCommented:
i ve tried telnet cluster2.eu.messagelabs.com 25 ( mx for ipspain ) and got that the port is open . if they block your ip you should contact them to see if they have any logs for blocking your IP in theire system .
or investigate in your side too it may be there .
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MbhushanCommented:

Did IPv6 is disabled. If Not, Please Disable IPv6 and check.

To Disable IPv6
http://technet.microsoft.com/en-us/network/cc987595.aspx 

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danigomeAuthor Commented:
I've disabled IPv6 but not succeed.
I think my IP has been banned from cluster2.eu.messagelabs.com, because I've tried from other IP and telnet to cluster2.eu.messagelabs.com 25 succeed.
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MbhushanCommented:
Download SMTPDiag Tool From Microsoft Website. Extract the tool into a folder. Open Command Promt and navigate to that folder and rin

smtpdiag "snderMailaddress" recipentAddress: /v

If IP blocked, it throw error.
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danigomeAuthor Commented:
The IP is blocked I'm afraid...
Error
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MbhushanCommented:
This clearly indicate, your domain or Public IP is blocked by their SMTP server. U have to check your Domain Blacklisted by which RBL by Sites like Mxtoolbox and others. and drop RBL builder to unblock ur domain. It took 24 -48 Hours.    
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