Server can successfully send but not receive e-mail, no errors in mail.log

SYSTEM INFORMATION
OS type and version Ubuntu 22.04
Webmin version 2.105
Virtualmin version 7.10.0

E-mails get sent out (to another server) successfully by both Usermin and the PHP mailing script deployed on the webserver.

However, incoming mails seem to not get delivered to the server’s mailboxes even though Postfix seems to be unaware of any problems:

Apr  9 23:43:24 virtualmin postfix/smtpd[504838]: connect from localhost[127.0.0.1]
Apr  9 23:43:24 virtualmin postfix/smtpd[504838]: A0F3C101A1A: client=localhost[127.0.0.1]
Apr  9 23:43:24 virtualmin postfix/cleanup[504841]: A0F3C101A1A: message-id=<1712695404.504861@example-domain.lv>
Apr  9 23:43:24 virtualmin postfix/smtpd[504838]: disconnect from localhost[127.0.0.1] helo=1 mail=1 rcpt=1 data=1 quit=1 commands=5
Apr  9 23:43:24 virtualmin postfix/qmgr[332281]: A0F3C101A1A: from=<janis@example-domain.lv>, size=985, nrcpt=1 (queue active)
Apr  9 23:43:24 virtualmin postfix/local[504870]: A0F3C101A1A: to=<janis.exampledomain@example-domain.lv>, orig_to=<janis@example-domain.lv>, relay=local, delay=0.07, delays=0.05/0.01/0/0.01, dsn=2.0.0, status=sent (delivered to command: /usr/bin/procmail-wrapper -o -a $DOMAIN -d $LOGNAME)
Apr  9 23:43:24 virtualmin postfix/qmgr[332281]: A0F3C101A1A: removed

I tried sending to the server’s mailboxes by both the Usermin (sending an e-mail to myself) and by the PHP mailing script deployed on that same server.

The Usermin shows the sent e-mails all right, displaying their location at /home/exampledomain/homes/janis/Maildir/.Sent, taking up 4.89 KiB. Drafts and Trash taking up 0 bytes. All of them being directories. The Inbox location is displayed as /home/exampledomain/homes/janis/, being a file, and taking up 4 KiB (which, I suppose, is some initial size).

I looked inside directory /home/exampledomain/homes/janis/Maildir/, and I see there are also directories “cur” and “new”, the latter being full of files containing all the e-mails that Usermin won’t display.

Is Usermin using Dovecot to display the messages? Could this mean that Dovecot is the one that’s somehow misconfigured and see only Sent and Trash but does not know where the incoming e-mail files are stored?