On 3/31/21 1:07 PM, Jon Baron wrote:
I run a mailing list with 4000 subscribers (firstname.lastname@example.org). Every time it sends mail to the list I get about 10 failure messages (completely failure, not temporary failure that keeps mail in the queue) saying that the host is not found or the email address doesn't exist. I can often find the host with the (linux) "host" command, and the email address checker often shows that the address is valid. The same email address that failed usually succeeds on the next post.
I would like to keep these messages in the queue if possible, or maybe allow more time for finding the host, or something, before giving up on the first try. I cannot find a configuration option.
This is not a Mailman issue. It is between your outgoing MTA and the recipient domain's MX MTA. If there is a solution, it will be in your MTA. I do note that Postfix smtp at least considers "Host or domain name not found." to be a retryable error, however if smtpd_recipient_restrictions includes reject_unknown_recipient_domain (which is definitely recommended against for Mailman) the mail will be rejected by Postfix during delivery from Mailman to Postfix.
As an example, this list's server (mail.python.org) defines a separate port in master.cf for Mailman to use with these settings:
127.0.0.1:8027 inet n - - - - smtpd -o smtpd_authorized_xforward_hosts=127.0.0.0/8 -o mynetworks=127.0.0.0/8 -o smtpd_recipient_restrictions=permit_mynetworks,reject -o smtpd_client_restrictions= -o smtpd_helo_restrictions= -o smtpd_sender_restrictions= -o smtpd_data_restrictions= -o smtpd_milters=inet:127.0.0.1:8891
(The milter on port 8891 is for opendkim signing)
Thus we do effectivly no checks on delivery from Mailman to Postfix and leave it up to Postfix outgoing smtp to handle things like domain not found.