Emails sent through a mailing list (mailman) to external mailboxes (Gmail, Outlook, Yahoo!, etc.) are not received
One of the following error messages appears in
NOQUEUE: reject: RCPT from localhost[127.0.0.1]: 554 5.7.1
The localhost IPv4 and IPv6 addresses are not whitelisted.
Add localhost IPv4 127.0.0.1 and IPv6 ::1/128 addresses to the white list:
Note: By applying the following solution, the limits on outgoing mail will not work.
Go to Tools & Settings > Mail Server Settings > White List
Click Add Network > add 127.0.0.1 to the IP address/mask field > click OK
Click Add Network > add ::1/128 to the IP address/mask field > click OK