Using Thunderbird POP3 SMTP Ubuntu 14.04 on my PC. Can't send messages but can receive. Error message is "4.4.0 ... Relaying temporarily denied. Cannot resolve PTR record for" Am only able to send messages to myself using ISP address.

Have reinstalled Thunderbird on PC and changed DSL router and spoken to ISP who can't see problem from their end but problem persists. Installed alternate email client Claws POP3 on same PC. Same problem as Thunderbird. Changed SMTP Port from 25 to 587, get different error message "mail server responded: 5.7.0 Authentication required"

Changed to laptop from PC and installed Thunderbird POP3 Ubuntu 12.04 on laptop which works perfectly. Seems that problem must be in Ubuntu/Thunderbird on my PC.

Appreciate any help. Thank you.

1 Answer 1


This problem has nothing to do with Thunderbird. In an effort to fight spam servers are tightening up their requirements. One of the standard requirements for relaying is that the IP address has a PTR record, often with the additional requirement that it passes rDNS validation. Some servers will freely forward for servers from IP addresses they consider local. It appears that your relay (SMTP) server does not relay for your IP address.

If you are using your ISP's relay, you should configure Thunderbird to connect to the Submission (587) port and authenticate with your credentials. It is rare that a server will relay an email received on the Submission port without authentications. If they do, it should only be from IP addresses that are local to the server. You can configure the credentials when you define the SMTP server used for sending emails. You can also add or modify them from the Account Settings menu in Thunderbird.

See the Outgoing section of my Email Policy for more details on restrictions that may be in place.


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