Hi, my configuration is as follows:
centos 4.2 rpm with all in defaults
caching nameserver
/etc/hosts
127.0.0.1 localhost.localdomain localhost
192.168.93.128 internal.localdomain internal
200.75.247.195 centos.myvnc.com

the address 200.75.247.195 is the NATed address controlled by the firewall.

is there any additional settings that must be modified to allow sending/receive mails for the MTA? as well as the web client?

when sending with the web client i got this error:

msg - SMTP server reported: Invalid Addresses;
nested exception is:
class com.sun.mail.smtp.SMTPAddressFailedException: 451 <eperez@centos.myvnc.com>: Temporary lookup failure
com.zimbra.cs.mailbox.MailServiceException: SMTP server reported: Invalid Addresses;
nested exception is:
class com.sun.mail.smtp.SMTPAddressFailedException: 451 <eperez@centos.myvnc.com>: Temporary lookup failure
at com.zimbra.cs.mailbox.MailServiceException.interna l_SEND_FAILURE(MailServiceException.java:327)
at com.zimbra.cs.mailbox.MailServiceException.SEND_FA ILURE(MailServiceException.java:339)
at com.zimbra.cs.service.mail.SendMsg.sendMimeMessage (SendMsg.java:324)
at com.zimbra.cs.service.mail.SendMsg.sendMimeMessage (SendMsg.java:165)
at com.zimbra.cs.service.mail.SendMsg.sendMimeMessage (SendMsg.java:154)
at com.zimbra.cs.service.mail.SendMsg.handle(SendMsg. java:107)
at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEng ine.java:252)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:163)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:84)
at com.zimbra.soap.SoapServlet.doPost(SoapServlet.jav a:228)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:709)
at com.zimbra.cs.servlet.ZimbraServlet.service(Zimbra Servlet.java:152)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:802)
at org.apache.catalina.core.ApplicationFilterChain.in ternalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.do Filter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invo ke(StandardWrapperValve.java:214)
at org.apache.catalina.core.StandardContextValve.invo ke(StandardContextValve.java:178)
at org.apache.catalina.core.StandardHostValve.invoke( StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke (ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invok e(StandardEngineValve.java:107)
at org.apache.catalina.valves.AccessLogValve.invoke(A ccessLogValve.java:526)
at org.apache.catalina.connector.CoyoteAdapter.servic e(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(H ttp11Processor.java:825)
at org.apache.coyote.http11.Http11Protocol$Http11Conn ectionHandler.processConnection(Http11Protocol.jav a:738)
at org.apache.tomcat.util.net.PoolTcpEndpoint.process Socket(PoolTcpEndpoint.java:526)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThr ead.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlR unnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:595)
Caused by: javax.mail.SendFailedException: Invalid Addresses;
nested exception is:
class com.sun.mail.smtp.SMTPAddressFailedException: 451 <eperez@centos.myvnc.com>: Temporary lookup failure

at com.sun.mail.smtp.SMTPTransport.rcptTo(SMTPTranspo rt.java:1141)
at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTr ansport.java:536)
at javax.mail.Transport.send0(Transport.java:151)
at javax.mail.Transport.send(Transport.java:80)
at com.zimbra.cs.service.mail.SendMsg.sendMimeMessage (SendMsg.java:243)
... 25 more

code - mail.SEND_FAILURE
method - ZmCsfeCommand.prototype.invoke
detail - soap:Sender
data - [object Object]