Help fixing Error: last request failed: [AUTH] Authentication failed.

The Error: last request failed: [AUTH] Authentication failed error can be caused by a range of things. It could be an incorrect DNS entry, a firewall or a misconfiguration. To help fix this problem you can follow our easy steps. They may or may not fix the problem. That’s because the problem can be caused by a wide scope of settings but it’s a good place to start.

A common place the last request failed error message is seen is inside the WHMCS POP3 Connection error email. If WHMCS can’t connect to your pop3 account that is used for support departments, WHMCS will send this email.

Can you see the Webmail Login Page?

Navigate to the domain you are trying to connect to (mail.domain.com) and navigate to domain.com. Can you see the website? If you use a cPanel server, can you see https://domain.com/webamil? If you can then this is not caused by an IP block. To be sure, white list the IP that is trying to connect to the server. If both accounts reside on the same server, this is not needed.

If you are unable to see the website or webmail page then this could be a few things;

Is your IP blocked in the server’s firewall?
Does your website resolve from another device?
Is Mod_Security blocking the connection?
Has cPHulk blocked your IP?

Can you Login to the email account?

So, at the /webmail login page, log in to the account. If you can log in, move on to the next section. But if you are trying to connect from an application like WHMCS or you can’t log in another way, follow the points below.

Change the email accounts password and try again.
Delete email account and recreate. Try again.
Change the hostname if connecting to mail.domain.com for the server’s main IPv4.
Check DNS records. Are the correct IPs listed in the A records and MX records?

Have you used the cPanel Transfer Tool?

If you have recently used the cPanel transfer tool to migrate a website you may have a DNS issue. You might see the login screen but the password is always incorrect. The transfer tool updates DNS records to proxy traffic. So, check the DNS records to make sure the correct IPs are listed.

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