451 Can't connect to - psmtp
Posted by on 10 June 2014 01:26 PM

Sending Mail Transfer Agent (MTA) cannot send messages due to error:
451 Can't connect to - psmtp

Possible Resolutions:

1) The receiving mail server is misconfigured in Postini. - or -
2) The receiving mail server is down - or -
3) There is some sort of network trouble between the receiving server and the Postini servers. - or -
4) The customer has a connection limit set that has been exceeded. (check this first) - or -

5) The user to which the e-mail is being sent to is an org that is under an e-mail config org. In this case move this user org under e-mail config org.

[Replace with the name of the domain whose traffic is being deferred.]

Troubleshooting steps:
1) Make sure the DNS MX records for the domain is routing to Postini
2) Check to make sure that the firewall/router protecting the mail server will accept TCP/IP connections from the Postini server IP range(s) associated with the Postinisystem which processes the mail traffic. For IP ranges, please see the solution entitled "Postini System IP Addresses ".
3) Make sure that TCP/IP packets can be sent to Postini:

[Replace N with the number of the System that processes your mail flow. This traceroute should get at least as far as or, but may trail off without completion inside Savvis or AT&T.]

4) Check the Delivery Mgr of the Postini Admin Console to make sure the delivery server is configured properly:
a) Go to Orgs and Users > Orgs and select the email config.
b) Go to Inbound Servers > Delivery Manager.
c) Look at the configured mail server (e.g.
d) If the mail server is incorrect or blank, type in the name of the correct mail server.
e) If there is a Conn. Limit imposed, but your mail server can handle more traffic, then increase the limit.
f) Click on the "Submit" button

5) Make sure the mail server for the domain is working.
a) Telnet to port 25 of the server:
telnet 25
b) If there is no response, then either the mail server is down or there is some sort of firewall or mail server configuration blocking the TCP/IP connection. Postini waits for 225 seconds for the receiving mail server to respond before returning the 451 to the sending MTA.

6) Check the Delivery Mgr to see if a connection limit has been set and see if the customer is exceeding it:
a) Go to Orgs and Users > Orgs and select the email config.
b) Go to Inbound Servers > Delivery Manager.
c) Look at the configured mail server (e.g.
d) See if there is a "Conn Limit" configured. If so, look at the status listed above the limit. If the customer is over the limit, messages will be deferred with the above error. 


Note: 451 is a non-fatal error. The sending MTA should retain and resend the message for 5 days before permanently bouncing the message.

ERROR: This domain name does not match domain registered in the license key file (, allowed domains:,localhost, please change the product path to match the domain under Admin CP > Settings > General Settings
This product will not work properly unless untill that value is changed.

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