Exchnage Server 2010 mail delivery issue

We have been experiencing more often mail delivery  issues  . specially incoming   . what are the in build tools I can used to troubleshoot similar issues   quickly  . first I want to make sure that email exchange level receive or not confirmation before going into the Telco level . I know lost of mail theses days got block out side the mail server  . I really want to know the right approach in the step by step way .
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Look at the exchange logs to see what is going on.  Your issue might be that you are not handling email to prevent being inundated with emails to individuals that do not exist thus leading to your queue build up.

Look at mail flow trace reports. You have yet to clearly outline what you think your issue is.
Is it outgoing emails or incoming?

make sure your email server is accessible from the outside. if you can provide your domain name, it would be simple to check whether your server is accepting external connection or whether it is even reachable.
curAuthor Commented:
both outgoing and incoming . this issue will not come all ways . please let me know command to check the external connection and the other connectivity testing commands
First, Look at your email's Error logs, event logs to see whether it is reporting any errors.
nslookup -q=mx yourdomain.com
You should get a listing of MX records.
telnet <servername in MX record> 25
what do you get? Do you get a 2xx servername ?
If you get a 4xx  (temporary error try again later) or a 5xx (permanent failure do not attempt again).

Post your domain name if you can.
If you can not, use www.mxtoolbox.com to lookup your domain's MX records and then use the smtp test to see whether your MX record server is accessible.
This will only test connectivity and whether your mail server is an open relay.  It will not deal with determining the underlying cause of your issue unless your server is an open relay and could explain the issues you are facing, i.e. your server is being misused to send out spam, and the large amount of email is taking a long time to process delaying your incoming handling while at the same time leading to your server to be blacklisted by others to an extent where your connections are denied/delayed.
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curAuthor Commented:
I had a issue with 3 emails . one was cleared after our Telco mail gateway confirm that block due to spam . other two of the email addresses email not reach the GW Logs even . these two senders in two different countries and hard to get come feedback . how can I move on the two emails addresses are not reaching our GW . please advice me to resolve this issue . theses two emails are very critical to our business
The only thing you can and should do to make sure your setup is functional and is not a constituting factor to the issues you are seeing.

If something is not making its way to your system, the only thing you can do is monitor your system to make sure it is always available, only the sending site can provide the information you need to determine what if any factor your setup is if at all.
Look at the public MX record. If you have or had your domain hosted on different providers, make sure only one has your records as authoritative.

I.e. ISP1 used to handle your public domain, but now ISP2 is doing it.
Make sure the ISP1 have removed your domain as authoritative with them.
For the above, you have to make sure you are contacting the correct one for removal.
curAuthor Commented:
most of the cases gateway level spam filter issues .do we have any way to check the free email providers support in case of troubleshooting purpose . we have few users are complaining they are not getting email free email created accounts .
The only thing you can do and should do is to make sure you have logging enabled on the incoming SMTP and outgoing side.
You have to also make sure your external smtp proxy if any have logging enabled as well.
Using the combination of the crunched logs you can determine from each:

The outgoing exchange/smtp proxy provide you access to information on how a message originating from your users to the point of when it is handed off to the next server.  here is liittle you can do dealing with free email providers.  Only their user having this information can try (checking their own bulk mal/filtering rules trash to make sure they do not have mistakenly blacklisted your email/domain.

Similarly on the incoming, the only information you can see is connections being made to each and if a connection is seen on he outside but it does not make it through to the exchange, the issue with that connection should have a log entry on whether your side denied/rejected  the connection from being passed.

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