Hi,I got a problem whereby Exchange Edge can receive email from Internet but cannot send email to outside. All email in the queue (Exchange Edge). In the Queue Viewer Indicated last error:-451 4.4.0 Primary target IP address responded with "421 4.2.1 Unable to connect". Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts.I have enabled logging in the Send Connector -Internetthis is the result:-#Software: Microsoft Exchange Server#Version: 8.0.0.0#Log-type: SMTP Send Protocol Log#Date: 2009-07-31T09:03:21.734Z#Fields: date-time,connector-id,session-id,sequence-number,local-endpoint,remote-endpoint,event,data,context2009-07-31T09:03:21.734Z,Internet,08CBDFD17F255B8E,0,,216.39.53.2:25,*,,attempting to connect2009-07-31T09:03:27.812Z,Internet,08CBDFD17F255B82,0,,209.85.222.69:25,*,,attempting to connect2009-07-31T09:03:32.125Z,Internet,08CBDFD17F255BB2,0,,202.190.203.180:25,*,,attempting to connect2009-07-31T09:03:42.734Z,Internet,08CBDFD17F255B8E,1,,216.39.53.2:25,*,,"Failed to connect. Error Code: 10060, Error Message: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 216.39.53.2:25"2009-07-31T09:03:42.734Z,Internet,08CBDFD17F255B8E,0,,216.39.53.3:25,*,,attempting to connect2009-07-31T09:03:48.750Z,Internet,08CBDFD17F255B82,1,,209.85.222.69:25,*,,"Failed to connect. Error Code: 10060, Error Message: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 209.85.222.69:25"2009-07-31T09:03:48.750Z,Internet,08CBDFD17F255B82,0,,209.85.218.43:25,*,,attempting to connect2009-07-31T09:03:53.125Z,Internet,08CBDFD17F255BB2,1,,202.190.203.180:25,*,,"Failed to connect. Error Code: 10060, Error Message: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 202.190.203.180:25"2009-07-31T09:03:53.125Z,Internet,08CBDFD17F255BB2,0,,202.75.41.58:25,*,,attempting to connect2009-07-31T09:04:03.734Z,Internet,08CBDFD17F255B8E,1,,216.39.53.3:25,*,,"Failed to connect. Error Code: 10060, Error Message: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 216.39.53.3:25"2009-07-31T09:04:03.734Z,Internet,08CBDFD17F255B8E,0,,68.142.202.247:25,*,,attempting to connect2009-07-31T09:04:06.437Z,Internet,08CBDFD17F255BB7,0,,209.85.26.191:25,*,,attempting to connectThe address space is SMTP - * with cost 1.Exchange edge is directly connect to the Internet without any server in front/web gateway. Previously the exchange edge is running fine until today it is unable to send email from Internal to External.Pls advise laiys

can you attempt a telnet session to the ip addresses listed above on port 25telnet 216.39.53.2 25

Tested cannot telnet. But i don't think that ip can telnet as i tried from my house without firewall blocking also failed to telnet.laiys

you should be able to connect to 216.39.53.2 on port 25, this is a yahoo serversomething is blocking port 25 between your edge server and the destinations

exchange edge to Internet port smtp is open. On the firewall rules, i saw the rules got traffic smtp going out.Now i'm blurred as i also suspect the same thing. But what causing it? I'm not sure.Tested sending to multiple domain (gmail, hotmail, yahoo, etc) but all stuck in the queue. On exchange edge, netstat -an got the resultDestination:------------------------69.89.31.140:25 SYN_SENT216.239.59.27:25 SYN_SENT65.55.92.136:25 SYN_SENT------------------------Anyway howto test that ISP is blocking port 25 or other issue?Pls advise. laiys

you may want to contact them at this pointcan an internal machine telnet to port 25 on any of these addresses

Nope.laiys

Hi Jim,Finally.solved.i've called ISP and clarify with them. They have blocked Port 25 and advise me to put smart host to their site when sending email.Thankslaiys