Connection Timed out Error for sender sending to our domain

Technical Details of permanent failure
Unspecified Error (Sent_message): Connection timed out
Above error always happens when sending to our domain but not to all. it only applies to some of the senders.
Senders are normally some gmail, yahoo or hotmail users.
it has been a week.
we are using sms for smtp 5.0.1 and using exchange 2003 sp2
anyone can help?
I tried to white list the sender also they got the same error.
connection timed out.
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JhunjoeAsked:
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JhunjoeConnect With a Mentor Author Commented:
I already got this problem solved.
it lies with the cisco firewall.
remove the inspect esmtp and it will solve this.
thanks.
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gupnitConnect With a Mentor Commented:
Hi,
Please go to www.mxtoolbox.com and conducts tests for your domain. Let me know the results, also what is the exact NDR
Thanks
Nitin Gupta (gupnit)
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JhunjoeAuthor Commented:
220 *************************************************************
Connect Time: 0 seconds - Good
Transaction Time: 1.156 seconds - Good
Relay Check: OK - This server is not an open relay.
Rev DNS Check: OK - xxx.125.xxx.xxx resolves to xxx.xxx.com.sg
GeoCode Info: Geocoding server is unavailable
Session Transcript: HELO please-read-policy.mxtoolbox.com
250 antispam Hello [64.20.227.13 [453 ms]
MAIL FROM: <test@mxtoolbox.com>
250 test@mxtoolbox.com....Sender [234 ms]
RCPT TO: <test@mxtoolbox.com>
550 Unable to relay for test@mxtoolbox.c [234 ms]
QUIT
221 shield Service closing transmission chann [234 ms]
 
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JhunjoeAuthor Commented:
exact NDR is
Technical details of permanent failure:
Unspecified Error (Sent_MESSSAGE)  : Connection Timed Out
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JhunjoeAuthor Commented:
I was wondering.
should i put our exchange server IP  in the MX record when i never open port 25 for traffic to come in.
I got 2 MX records in external DNS
Preference Host Name IP Address TTL    
5 Antispam server 165.x.xx.xx  3600  ( this one is antispam server - port 25 enable in firewall )
10 Exchange server 165.x.xx.xx 3600 ( this one exchange server - port 25 disable in firewall )
Do you think if there is any problem with this MX record?
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jfromanskiConnect With a Mentor Commented:
Do you check Application Event Log on Exchange Server against this issue. What events was logged?
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