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Found the issue.. it was DNS taking time to get populated. Finally I got the mails through the filtering server.
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Found the issue.. it was DNS taking time to get populated. Finally I got the mails through the filtering server.

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We register two domain: domainA and domainB.<br />
Both domains have the identical A record (public IP) pointing to our single Exchange 2010 server, where both domains are also &quot;accepted domains&quot; there. <br />
&nbsp;<br />
But only domainA has a MX record (public IP), which points to the above Exchange 2010 server. <br />
Now I just added to domainB a new MX record (public IP) which points to a 3rd party filtering server, for a testing purpose. <br />
To my surprise, from email header I can tell the emails intended to be sent to domainB are directly going into the single Exchange 2010 server instead of the 3rd party filtering server. Isn't it right the emails should follow the MX record? Even both Domain A and B are with the same A record and are accepted domain by the Exchange, the MX record should be the decisive factor for emails to be sent to, right?<br />
I must have missed something here. Can you shed some light?<br />
<br />
<br />
ed to use domainB for some testing purpose<br />
<br />
<br />
I was taught that My questions to you are:
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We register two domain: domainA and domainB.
Both domains have the identical A record (public IP) pointing to our single Exchange 2010 server, where both domains are also "accepted domains" there. 
 
But only domainA has a MX record (public IP), which points to the above Exchange 2010 server. 
Now I just added to domainB a new MX record (public IP) which points to a 3rd party filtering server, for a testing purpose. 
To my surprise, from email header I can tell the emails intended to be sent to domainB are directly going into the single Exchange 2010 server instead of the 3rd party filtering server. Isn't it right the emails should follow the MX record? Even both Domain A and B are with the same A record and are accepted domain by the Exchange, the MX record should be the decisive factor for emails to be sent to, right?
I must have missed something here. Can you shed some light?


ed to use domainB for some testing purpose


I was taught that My questions to you are:

Why didn't emails follow MX record?

Within Internet message handling services (MHS), a message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture. A MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol (SMTP). The terms mail server, mail exchanger, and MX host may also refer to a computer performing the MTA function. The Domain Name System (DNS) associates a mail server to a domain with mail exchanger (MX) resource records containing the domain name of a host providing MTA services.

Email Servers

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

The Domain Name System (DNS) is a hierarchical, globally distributed system responsible for associating the name of a computer, service or other resource into an IP address for connecting to the Internet or a private network. Most prominently, it translates domain names to the numerical IP addresses needed for the purpose of computer services and devices worldwide.

An email client, email reader or more formally mail user agent (MUA) is a computer program used to access and manage a user's email. A web application that provides message management, composition, and reception functions is sometimes also considered an email client, but more commonly referred to as webmail.