Postfix: unable to send emails - probably MariaDB (MySQL)

Debian 10.5; ISPConfig 3.1.15p3
Hello,
I am struggling with the following messages from the file "/var/log/mail.warn".

Code:

Aug  2 22:26:47 s2 postfix/smtpd[2333]: warning: connect to mysql server 127.0.0.1: Host '127.0.0.1' is not allowed to connect to this MariaDB server
Aug  2 22:26:47 s2 postfix/smtpd[2333]: warning: mysql:/etc/postfix/mysql-virtual_client.cf lookup error for "localhost"
Aug  2 22:26:54 s2 postfix/trivial-rewrite[2336]: warning: virtual_mailbox_domains: proxy:mysql:/etc/postfix/mysql-virtual_domains.cf: table lookup problem
Aug  2 22:26:54 s2 postfix/trivial-rewrite[2336]: warning: virtual_mailbox_domains lookup failure
Aug  2 22:26:54 s2 postfix/trivial-rewrite[2336]: warning: virtual_mailbox_domains: proxy:mysql:/etc/postfix/mysql-virtual_domains.cf: table lookup problem
Aug  2 22:26:54 s2 postfix/trivial-rewrite[2336]: warning: virtual_mailbox_domains lookup failure
Aug  2 22:26:54 s2 postfix/smtpd[2333]: warning: mysql:/etc/postfix/mysql-virtual_client.cf lookup error for "mx-out-01b.sjc3.discourse.cloud"

I suspect it's related to MariaDB (MySQL):

Code:

Aug  2 22:18:16 s2 postfix/proxymap[1212]: warning: connect to mysql server 127.0.0.1: Host '127.0.0.1' is not allowed to connect to this MariaDB server

I did run an upgrade today and it did upgrade MariaDB and Postfix

Code:

Start-Date: 2020-08-02  15:48:33
Commandline: apt upgrade
Requested-By: main (1000)
Install: linux-image-4.19.0-10-amd64:amd64 (4.19.132-1, automatic)
Upgrade: libpython3.7-minimal:amd64 (3.7.3-2+deb10u1, 3.7.3-2+deb10u2), perl-base:amd64 (5.28.1-6, 5.28.1-6+deb10u1), postfix:amd64 (3.4.10-0+deb10u1, 3.4.14-0+deb10u1), libdbus-1-3:amd64 (1.12.16-1, 1.12.20-0+deb10u1), linux-libc-dev:amd64 (4.19.118-2+deb10u1, 4.19.132-1), postfix-mysql:amd64 (3.4.10-0+deb10u1, 3.4.14-0+deb10u1), grub-common:amd64 (2.02+dfsg1-20, 2.02+dfsg1-20+deb10u2), dbus:amd64 (1.12.16-1, 1.12.20-0+deb10u1), mariadb-common:amd64 (1:10.3.22-0+deb10u1, 1:10.3.23-0+deb10u1), speedtest-cli:amd64 (2.0.2-1, 2.0.2-1+deb10u1), perl-modules-5.28:amd64 (5.28.1-6, 5.28.1-6+deb10u1), mariadb-server-core-10.3:amd64 (1:10.3.22-0+deb10u1, 1:10.3.23-0+deb10u1), libpython3.7:amd64 (3.7.3-2+deb10u1, 3.7.3-2+deb10u2), python3.7:amd64 (3.7.3-2+deb10u1, 3.7.3-2+deb10u2), grub2-common:amd64 (2.02+dfsg1-20, 2.02+dfsg1-20+deb10u2), grub-pc:amd64 (2.02+dfsg1-20, 2.02+dfsg1-20+deb10u2), libpython3.7-stdlib:amd64 (3.7.3-2+deb10u1, 3.7.3-2+deb10u2), postfix-doc:amd64 (3.4.10-0+deb10u1, 3.4.14-0+deb10u1), python3.7-minimal:amd64 (3.7.3-2+deb10u1, 3.7.3-2+deb10u2), mariadb-server-10.3:amd64 (1:10.3.22-0+deb10u1, 1:10.3.23-0+deb10u1), libperl5.28:amd64 (5.28.1-6, 5.28.1-6+deb10u1), grub-pc-bin:amd64 (2.02+dfsg1-20, 2.02+dfsg1-20+deb10u2), clamav-docs:amd64 (0.102.3+dfsg-0+deb10u1, 0.102.4+dfsg-0+deb10u1), linux-image-amd64:amd64 (4.19+105+deb10u4, 4.19+105+deb10u5), clamav:amd64 (0.102.3+dfsg-0+deb10u1, 0.102.4+dfsg-0+deb10u1), clamav-daemon:amd64 (0.102.3+dfsg-0+deb10u1, 0.102.4+dfsg-0+deb10u1), clamdscan:amd64 (0.102.3+dfsg-0+deb10u1, 0.102.4+dfsg-0+deb10u1), clamav-freshclam:amd64 (0.102.3+dfsg-0+deb10u1, 0.102.4+dfsg-0+deb10u1), mariadb-client-10.3:amd64 (1:10.3.22-0+deb10u1, 1:10.3.23-0+deb10u1), mariadb-server:amd64 (1:10.3.22-0+deb10u1, 1:10.3.23-0+deb10u1), libunwind8:amd64 (1.2.1-9, 1.2.1-10~deb10u1), mariadb-client-core-10.3:amd64 (1:10.3.22-0+deb10u1, 1:10.3.23-0+deb10u1), mariadb-client:amd64 (1:10.3.22-0+deb10u1, 1:10.3.23-0+deb10u1), libmariadb3:amd64 (1:10.3.22-0+deb10u1, 1:10.3.23-0+deb10u1), libgnutls30:amd64 (3.6.7-4+deb10u4, 3.6.7-4+deb10u5), perl:amd64 (5.28.1-6, 5.28.1-6+deb10u1), clamav-base:amd64 (0.102.3+dfsg-0+deb10u1, 0.102.4+dfsg-0+deb10u1), libclamav9:amd64 (0.102.3+dfsg-0+deb10u1, 0.102.4+dfsg-0+deb10u1), base-files:amd64 (10.3+deb10u4, 10.3+deb10u5)
End-Date: 2020-08-02  16:03:34

I am able to connect to the database

Code:

root@s2:/# mysql dbispconfig -uispconfig -p
Enter password:
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 350
Server version: 10.3.23-MariaDB-0+deb10u1-log Debian 10

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [dbispconfig]> show tables;
+--------------------------+
| Tables_in_dbispconfig    |
+--------------------------+
| aps_instances            |
| aps_instances_settings   |

[...SNIP...]

I am able to receive e-mails. This works in an IMAP client (tested with Firefox) and with Roundcube.
But sending an e-mail gives me the following error:

Code:

SMTP-fout (451): Ontvanger "********@gmail.com" kan niet toegevoegd worden (4.3.5 <localhost[::1]>: Client host rejected: Server configuration error).

Note: I did mask the receiver (ontvanger) with asterisks.
I did try quite some things but I can't find a solution. Some help would be very much appreciated. Thanks.

 

Yes, I see the error. I will check the config.

Code:

root@s2:/# mysql -h 127.0.0.1 -u ispconfig -p dbispconfig
Enter password:
ERROR 1130 (HY000): Host '127.0.0.1' is not allowed to connect to this MariaDB server

 

I might have found it. I commented out the line "skip-name-resolve" in the file "50-server.cnf". The file is located in the folder "/etc/mysql/mariadb.conf.d". Next I did restart MariaDB ("service mysql restart") and connected successfully to 127.0.0.1 as instructed by Till.

[EDIT]
Confirmed: this works for me. Hopefully this is helpful for anyone running into this after installing updates for Debian 10.
Thanks Till for you help.
[/EDIT]