Question Incoming mail stays in queue permanently

[Bamboo Toothbrush]

Hello all
I've configured a mail account on a new instance of Plesk Onyx. Outgoing mail is fine, using webmail or a mail client. But incoming mail is permanently queued, no matter who the sender is.
If you have any suggestions I would love to hear them.
Many thanks

From /var/logmaillog (email addresses anonymised here):
Aug 8 08:27:11 d qmail-queue-handlers[30194]: from=sender@example.com
Aug 8 08:27:12 d qmail-queue[30200]: scan: the message(drweb.tmp.hCxye0) sent by sender@example.com to recipient@example.com is passed
Aug 8 08:27:12 d qmail: 1502137632.284651 info msg 934819: bytes 3105 from <sender@example.com> qp 30202 uid 2020
Aug 8 08:27:12 d qmail-local-handlers[30203]: from=sender@example.com
Aug 8 08:28:53 d qmail-local-handlers[31278]: from=sender@example.com
Aug 8 08:33:53 d qmail-local-handlers[31406]: from=sender@example.com
Aug 8 08:42:13 d qmail-local-handlers[31614]: from=sender@example.com
Aug 8 08:53:53 d qmail-local-handlers[31735]: from=sender@example.com
Aug 8 09:08:54 d qmail-local-handlers[451]: from=sender@example.com
Aug 8 09:27:13 d qmail-local-handlers[595]: from=sender@example.com
Aug 8 09:48:53 d qmail-local-handlers[781]: from=sender@example.com

 

[UFHH01]

Hi Bamboo Toothbrush,

Plesk comes with a great "Plesk Repair Utility" ( => Plesk Repair Utility ), with which you are able to investigate and resolve quite a lot of issues/errors/problems.

An example command to repair "mail" - related issues, could be:

plesk repair mail -y -v

( If you need further informations/command options, pls. consider to read the above mentioned official Plesk documentation )​

In addition, pls. inform yourself about needed open ports on your server at:

=> Which Ports Need To Be Opened for all Plesk Services to Work with a Firewall?​

Another option is to switch from qmail to postfix - usage and back to qmail - usage again, to solve common issues or/and misconfigurations:

plesk installer --select-product-id plesk --select-release-current --install-component postfix

plesk installer --select-product-id plesk --select-release-current --install-component qmail

 

[Bamboo Toothbrush]

Thank you UFHH01 for your advice.
According to the Plesk support people, it turns out to be this error, as yet unresolved for me:
Unable to receive e-mails with Dovecot: Error: userdb lookup: connect(/var/run/dovecot/auth-userdb) failed: Permission denied