We are having this problem on some servers, Sometimes the bounce user does not create Maildir itself. So I created the mail directory and gave permission manually. Still, the error is there. The bounce user and passwords are correct in the configuration.
I am using LInode.com and Digitalocean.com. Linode servers are working fine, But the problem is in digitalocean. It is from ubuntu 16.04 lts.
Please provide me with a solution ASAP.
Cannot create POP3 connection to mail.123.xyz: Can't login to this server Identifying consecutive bounces
You would need to think about the mailbox creation as a separate problem from the phpList configuraton.
Using whatever method is available on the server, create the bounce mailbox, with user and password. If your issue is that the mailbox is not created properly, I would suggest that you use whatever graphical interface there might be to create the mailbox (i.e. cpanel). Once you can create the mailbox, and send a message to it, and it is received, then you would want to configure the connection of phpList to check the mailbox, which it sounds like you know how to do (Linode is working).