I noticed somehow that mail from Cpanel does not open through the Web Roundcube, SquirrelMail, Horde, and also you can’t connect to mail from PHP scripts.
In the logs /var/log/maillog I saw the following error:
Dec 14 13:21:04 hostname dovecot: auth: Error: Cpanel::MailAuth: cphulk blocked login for user ‘firstname.lastname@example.org’ to access service ‘mail’ from IP ‘::1’
As it turned out, access to mail was blocked by cPHulk.
The protection against attacks based on the username has worked.
If you want to block attacks only by IP addresses, then you can basically turn it off by opening the “WHM” – “Protection against attacks using cPHulk” panel, turn off the switch next to “Protection based on username” and click the “Save” button below.
Current locks can be removed by opening the Log Reports tab – Delete Blocks and Clear Reports.