Hello, 

I have problem with new installed Exchange 2013 Server, I can receive mails from outside organization, but can not send mails on gmail.com yahoo.com hotmail.com, outlook.com and etc.

mails are in queue list with 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.  

Exchange server failed to connect to target SMTP server on port 25. Likely DNS problem (cannot resole names of target domain) or firewall problem (blocking outbond connection on port 25).

Hello, i have speak with my ISP they have opened port 25. we have made port forwarding for port 25,

But i have tried some another mail servers, and mail was send, but with this domains i have problems, i recieving mails from them but cant to reply, or send new mail!

451 4.4.0 Error encountered while communicating with primary target IP address: ""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. The last endpoint attempted was 66.220.159.18:25"

Port forwarding is inbound. I'm talking about outbound.

451 4.4.0 Error encountered while communicating with primary target IP address: ""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. The last endpoint attempted was 66.220.159.18:25"

Check your DNS. I'm totally basing this on the fact that you didn't mention a facebook at all in your email and that looks like that resolves to some facebook address:

> 66.220.159.18
Server:  b.resolvers.Level3.net
Address:  4.2.2.2

Name:    msgin-shv-08-frc3.facebook.com
Address:  66.220.159.18

Hi Daniel,

Thank you for your question.

Did you mean that you could send email to all external domains?

Did you have Exchange hosting environment?

We should make sure we could ping those external domains from internal.

Use the following command to make sure  all Exchange server component state is active:

Get-ServerComponentState Identity <servername>

Then disable A/V to check if the issue persist.

We could refer to the following link to test outbound message following:

https://testconnectivity.microsoft.com/

In addition, we could check trace message log.

If there are any questions regarding this issue, please be free to let me know.

Best Regard,

Jim