The following error appears in MailEnable logs (
%plesk_dir%\Mail Servers\Mail Enable\Logging), while senging message from webmail to remote server:
There was an error sending your message: Failed to add recipient: email@example.com [SMTP: Invalid response code received from server (code: 503, response: This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server.)]
SMTP authentication is required by the server, by default. Mail client is not configured to use SMTP autentication on outgoing SMTP server.
Ensure that Inbound SMTP authentication is not enabled.
Go to MailEnable > Servers > localhost > Services and Connectors > SMTP > Properties > Advanced SMTP > Inbound authentication and select
Do not require authentication under
Deliveries to local addresses: like shown below:
Temporarily disable SMTP authentication for local senders:
Go to SMTP > Properties > Relay > Allow Mail Relay and enable Allow relay for local sender address setting.
127.0.0.1to SMTP > Properties > Relay under Privileged IPs....
Note: using this configuration in a persistent manner can be a cause of outgoing spam.
Configure mail clients to use SMTP authentication. Refer to the following MailEnable KB article.