Incoming emails (either local or external) do not appear in Inbox on Plesk server

Symptoms

• Incoming emails (either local or external) do not appear in inbox.

• Messages appear like delivered in '/var/log/maillog', but at the same time, they are not stored in mailbox directory:

  /var/log/maillog.processed:Sep 11 09:30:41 pleskpostfix/smtpd[2317439]: 3FCFA63066: client=localhost.localdomain[::1], sasl_method=PLAIN, sasl_username=john.doe@example.com
  /var/log/maillog.processed:Sep 11 09:30:41 plesk postfix/cleanup[2320558]: 3FCFA63066: message-id=<76e4044d28cf71ddc99ade562fb76776@example.com>
  /var/log/maillog.processed:Sep 11 09:30:41 plesk postfix/qmgr[2282916]: 3FCFA63066: from=<john.doe@example.com>, size=570, nrcpt=1 (queue active)
  /var/log/maillog.processed:Sep 11 09:30:41 plesk postfix/pipe[2329805]: 3FCFA63066: to=<john.doe@example.com>, relay=plesk_virtual, delay=0.43, delays=0.39/0/0/0.04, dsn=2.0.0, status=sent (delivered via plesk_virtual service)
  

  root@plesk # grep -ir '76e4044d28cf71ddc99ade562fb76776' /var/qmail/mailnames/example.com/john.doe
  root@plesk # 
  

• Open file limits are set to default values:

  # root@plesk [~]# ulimit -a | grep "open files"
  open files (-n) 1024

• Plesk hosts a lot of mailboxes:

  # plesk db "select * from mail" | wc -l
  3538

Cause

• Bug in Plesk with ID #PPPM-15120.

Resolution

Until bug is fixed, apply the following workaround to increase the limits for the open files:

1. Connect to the server via SSH

2. Run the command to increase limits:

   # ulimit -n 16384

3. Execute the command to regenerate configuration files for mail:

   # plesk sbin mchk