Problem with POP3 login after upgrade to latest release

[dexus]

Imidiately after upgrade to latest cPanel release problems with POP3 started.

From time to time some email account can't login, and server reports error...

"ERR Temporary problem, please try again later"

maillog is showing the following...

Dec 23 09:08:39 myhost pop3d-ssl: LOGIN FAILED, user=*email@address_com*, ip=[::ffff:*IP_removed*]
Dec 23 09:08:39 myhost pop3d-ssl: authentication error: Input/output error

That mail account is working, and it can succesfully login a minute before this error, and minute after this, I have no idea why it reports this error for any email account at least once per hour.

This never happend before.

[cpanelnick]

Imidiately after upgrade to latest cPanel release problems with POP3 started.

From time to time some email account can't login, and server reports error...

"ERR Temporary problem, please try again later"

maillog is showing the following...

Dec 23 09:08:39 myhost pop3d-ssl: LOGIN FAILED, user=*email@address_com*, ip=[::ffff:*IP_removed*]
Dec 23 09:08:39 myhost pop3d-ssl: authentication error: Input/output error

That mail account is working, and it can succesfully login a minute before this error, and minute after this, I have no idea why it reports this error for any email account at least once per hour.

This never happend before.

Do you have pop and imap monitoring enabled inside of the service manager in WHM?

[dexus]

Yes, and that is not a problem, they have never been failed or restarted.

[dexus]

I increased now "Number of Authentication Daemons" to 5 (it was 2 by default) in "WHM > Mailserver Configuration" and this problem did not appeared again in last two hours...

Now I am little confused with this, this is a server with only 3 domains and only 20 email accounts, and this default Authentication Daemons was obviously not enough... Why?

Is that mean that on servers with 500 domains and 1000+ email accounts we should set this to 100+ or what...???