550-Please turn on SMTP Authentication in your mail client

Operating System & Version
CENTOS 7.9
cPanel & WHM Version
v94.0.8

OttoM

Member
Apr 4, 2018
19
4
3
UK
cPanel Access Level
Root Administrator
Hi guys,

This email issue keeps happening very the last three months.

I'm using outlook to send emails and I do have the SMTP authentication enabled. Emails work fine and then out of the blue I keep getting emails back. When this happens all I can do to make it work again is go to Security Center » SMTP Restrictions and toggle the The SMTP restriction button on and off, meaning I disable the SMTP restriction and enable again. Then emails work again.

As this occurs very often now, I'd like to find a stable solution.

Could anyone suggest any solutions or help please?

many thanks
 

cPRex

Jurassic Moderator
Staff member
Oct 19, 2014
6,081
777
313
cPanel Access Level
Root Administrator
Hey there! The SMTP restriction tool in WHM isn't related to the SMTP authentication service that Outlook uses. The SMTP restriction tool controls what users and services on the machine can connect to the mail services, adding additional security to outbound email. This wouldn't change how Outlook connects to the server.

I also confirmed that toggling that process does not restart the Exim service.

In the past, I've always seen this be an issue with Outlook itself. Do you have any issues using a different client such as Thunderbird?
 

OttoM

Member
Apr 4, 2018
19
4
3
UK
cPanel Access Level
Root Administrator
Thank you for the clarification cPRex,

I haven't used Thunderbird, but I think I will try it next time I face this issue with Outlook.

Strange how toggling the disable/enable button on SMTP fixes the issue.
 

cPRex

Jurassic Moderator
Staff member
Oct 19, 2014
6,081
777
313
cPanel Access Level
Root Administrator
I also think that behavior is strange as well. If you're able to come up with a method to reproduce the issue reliably, feel free to submit a ticket to our team so we can check the server. You could also try checking the /var/log/maillog file to see if there are any odd errors there during the time of the authentication errors.
 
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