Exchange 2010 refused connection from sender

Dear Expert,

I have a customer that cant send email to us recently, the log they provided state below,

2013-12-24 17:29:22,OUTBOUND,jmchen@efgh.com.tw<mailto:jmchen@efgh.com.tw>(172.21.36.135),joyce@abc,com<mailto:joyce@abc,com>(101.99.x.x-mail.abc,com<http://101.99.x.x-mail.abc,com>),967613063,22545,QUEUED,601,Deferred: Connection refused by mail.abc,com<http://mail.abc,com>
2013-12-24 17:29:22,OUTBOUND,miahsieh@efgh.com.tw<mailto:miahsieh@efgh.com.tw>(172.21.36.135),joyce@abc,com<mailto:joyce@abc,com>(101.99.x.x-mail.abc,com<http://101.99.x.x-mail.abc,com>),513374723,53521,QUEUED,601,Deferred: Connection refused by mail.abc,com<http://mail.abc,com>
2013-12-24 17:29:22,OUTBOUND,jmchen@efgh.com.tw<mailto:jmchen@efgh.com.tw>(172.21.36.135),joyce@abc,com<mailto:joyce@abc,com>(101.99.x.x-mail.abc,com<http://101.99.x.x-mail.abc,com>),914463265,13973,QUEUED,601,Deferred: Connection refused by mail.abc,com<http://mail.abc,com>
2013-12-24 17:29:22,OUTBOUND,miahsieh@efgh.com.tw<mailto:miahsieh@efgh.com.tw>(172.21.36.135),joyce@abc,com<mailto:joyce@abc,com>(101.99.x.x-mail.abc,com<http://101.99.x.x-mail.abc,com>),1285071653,25209,QUEUED,601,Deferred: Connection refused by mail.abc,com<http://mail.abc.com>


I did check their domain name, the spf and reversed dns is not found.

could it be the cause?

remarks: only this customer is having problem to send email to us

Thanks
Alfred
patcheahAsked:
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Marcus BointonConnect With a Mentor Commented:
Notice that those errors in the logs are deferrals due to connection being refused, not bounces. "Connection refused" is not an SMTP-level issue - it's lower-level than that; I would check that they (or possibly their upstream ISP) are not blocking outbound SMTP. Blacklisting and reverse IP blocking typically happens within the SMTP layer, and should result in 5.1.7 status bounces, or at least 4.1.7 deferrals, neither of which are happening here.

A missing SPF is not a valid reason for rejection; the only basis for SPF rejection is a definitive 'FAIL' status, and many receivers (stupidly, since it defeats the entire point of it) do not even do that, and again, it's an SMTP-layer check and should result in a bounce. Insisting on matching reverse DNS is a reasonable anti-spam technique, but will often reject a mail from legitimate sources, such as gmail which often has mismatching reverse IPs (because they have such a high turnover of servers).
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dsnegi_25decCommented:
Yes ...........
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vSolutionsITConnect With a Mentor Commented:
Ask them to check if their email server's ip address is blacklisted or not. If yes then they will have to get it removed from the blacklists.
Do you have your email server's configured to check reverse DNS ? if yes then it could be the issue.
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MaheshArchitectCommented:
Yes, VSolutionIT is right..

Your Email server must be configured to check \ verify Sender's SPF record and if they don't have or got blacklisted, emails sent by them will be rejected by your server

Mahesh
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Pradeep VIshwakarmaCommented:
You must request a REVERSE DNS ENTRY from your ISP who issued the block of IP ADDRESSES.

The NAME and IP ADDRESS to which is mapped MUST EXACTLY MATCH THE HOSTNAME OF THE MAIL SERVER SENDING THE E-MAIL.

If you use one IP ADDRESS to send for multiple domains, make certain the mapping matches the domain name of your HOSTING COMPANY and the setup a PTR RECORD for each hosted domain in the DNS for the hosted domain.

You should also set up REVERSE DNS on your local DNS SERVERS and create a PTR record for each of the hosted domain's HOST records which maps to the MX record for the e-mail.
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patcheahAuthor Commented:
Thanks experts.

Request sender to add spf record. So far so good now. Happy New Year!
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