I am using Exchange 2013 Trail version. I am able to receive email from Internet. I have enabled the send connector with asterisk SMTP Domain in Address Space in Scoping. I have forwarded all the appropriate ports in my system.

NOTE: There is no PTR record set by my ISP.

Question: Port 25 is open when I check https://canyouseeme.org/ . With Telnet and Delivery Report I am assuming outgoing 25 port is being blocked by ISP? IF yes, then is there a work around.

I have tried NethServer (Linux Distribution), hMailServer windows setup. By using all these I can receive emails from internet but not able to send to internet. Locally I am able to send and receive emails.

And Let me know If you need any further information.

Telnet gmail.com 25

220 mail.primeq.gq Microsoft ESMTP MAIL Service ready at Mon, 21 Sep 2020 22:19:19 -0700
451 4.7.0 Timeout waiting for client input
Connection to host lost.

Exchange Admin Center -> mail flow -> delivery reports -> Delivery Report

The last attempt to send the message was at 9/21/2020 9:06:41 PM (UTC-08:00) Pacific Time (US & Canada) and generated the error '[{LED=451 excellbroadband-smtp Cannot connect to server []: Cannot assign requested address};{MSG=};{FQDN=};{IP=};{LRT=}]'.
  • 1
    Yes, most probably your hoster blocks outgoing connections on that port. That's common practice. Talk to your hoster. Sep 22, 2020 at 6:21
  • 2
    Your ISP has intercepted your outgoing port 25 connection and redirected it to its own server. You should upgrade to business class ISP service. We cannot support running servers on home network connections. Sep 22, 2020 at 10:51
  • Thanks for the reply. I believe you are right. How Can I mark an answer Any why my question got -1. What needs to be added more and what is reason for down vote.
    – ACE
    Sep 22, 2020 at 13:27

1 Answer 1


Make sure there're no rules blocking the port 25 in firewall, and ISP hasn't blocked your outgoing connection on port 25.

Please check if there were any NDR(undeliverable) messages sent to the senders' inbox folders. At the same time, you could also use the message tracking log to do a trace for these emails, maybe some events with source could help you find the reasons to cause the mailflow issue.

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