Authentication Blocking Outbound SMTP

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Joined: Tue Nov 12, 2019 1:13 am

Authentication Blocking Outbound SMTP

Post by Wallie » Tue Nov 12, 2019 5:58 pm

I am getting a 503 error and mail is being stopped the outbound smtp server. I am trying to send mail out through any domain that I have and the test at mxtool box showed the following that made me think it is an AUTHENTICATION conflict.

Does anyone have insight on what settings on the SMTP server?

SMTP Reverse DNS Mismatch OK - resolves to
SMTP Valid Hostname OK - Reverse DNS is a valid Hostname
SMTP Banner Check OK - Reverse DNS matches SMTP Banner
SMTP TLS OK - Supports TLS.
SMTP Connection Time 0.672 seconds - Good on Connection time
SMTP Open Relay OK - Not an open relay.
SMTP Transaction Time 2.609 seconds - Good on Transaction Time

Here is the session transcript from that test:

Connecting to

220 ESMTP MailEnable Service, Version: 10.27-10.27- ready at 11/12/19 12:39:58 [609 ms]
EHLO [], this server offers 3 extensions
250-SIZE 40960000
250 STARTTLS [609 ms]
250 Requested mail action okay, completed [609 ms]
503 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. [609 ms]

LookupServer 3125ms

Brett Rowbotham
Posts: 550
Joined: Mon Nov 03, 2003 7:48 am
Location: Cape Town

Re: Authentication Blocking Outbound SMTP

Post by Brett Rowbotham » Fri Nov 15, 2019 4:31 am

The server is doing exactly what it is meant to do to stop your server spewing spam all over the internet.

If your server received emails from an external source that were actually destined for an external receiver, and passed them on without doing anything to stop that (such as requiring authentication to send to external receivers), then you would be a spam creators dream.

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