SMTP Error: 550 Please turn on SMTP Authentication in your mail client – IP is not permitted to relay through this server without authentication

We had a customer complaining about a commonly seen error of the following type:

550 Please turn on SMTP Authentication in your mail client. mail-pf0-f172.google.com [209.85.192.172]:38632 is not permitted to relay through this server without authentication.

Diagnostic-Code: smtp; 550-Please turn on SMTP Authentication in your mail client. 550-mail-pf0-f172.google.com [209.85.192.172]:38632 is not permitted to relay 550 through this server without authentication.

reason: 550-Please turn on SMTP Authentication in your mail client.
550-mout.kundenserver.de [212.227.17.24]:49392 is not permitted to relay
550 through this server without authentication.

They were all basically the same error. This is a common error and the solution is pretty simple as it looks like. Enabling ‘SMTP Authentication’ on the outlook or the mail client should solve the problem. But interestingly, the client was smart and he wasn’t doing any mistake with ‘SMTP authentication’. The error was actually showing up when someone was trying to send the mail to him (As a receiver SMTP). We then tried digging the error further.

There is something we need to remember. SMTP is not only authenticated using username and password, it also goes through a dns authentication check too. If your dkim/domainkeys/spf/dmarc do not match as the mail server has advised, the mail will get denied with the same type of error (Error code 550). We then realized the customer account was transfered earlier from a different server and the old domainkeys were still there in it’s DNS zone file. As domainkeys are RSA keys generated per server, it is important to regenerate the keys after the server change. Otherwise, the old key check through the DNS can trigger the 550 error from the receiver relay. We had deleted and generated a new domainkeys for the customer and the error went off.

How to change WHM reseller password!

After all these years, it never came to my mind that when somebody purchases a reseller, they usually do not change their WHM password for a long period. They keep it ‘as it is’ generated by WHMCS on purchasing the reseller package. The most interesting fact is that they don’t change it, because they fail to find an option to change it in WHM.

WHM doesn’t come with a distinct option saying ‘Change WHM Password’ unfortunately. That makes a percentage of reseller believe that they can not change their WHM password. In recent times, while investigating a couple of reseller hacks, I could determine, one of the primary reason of password leakage is, not changing the WHM password for longer period of time and keeping it ‘saved’ in browser. At a certain point of time, when the browser gets exposed to the hacker, user loose control over their WHM account.

Now the question comes, how to change a WHM password! Your WHM username is basically a cpanel username. It only granted to be able to own multiple cpanel accounts and that is the only difference, that’s all. To change the WHM password, simply login to your cpanel with the WHM details and use the ‘Change Password’ option. So if your WHM url is http://something.com/whm with username: something and password: anything, then you basically login with the same details in http://something.com/cpanel instead of whm. Once logged in, just visit the Change Password to change your WHM/Reseller password.

It is highly recommended for all the users to change the password once they receive their reseller welcome email. You should try changing the reseller password often to prevent any anonymous leakage from unknown attacks. It is also advised not to save the WHM password in your browser. Please keep in mind, your password can leak access to the cpanel accounts under you and cause great threat for their websites & domain reputation. They possibly have no reason to be so.