Why does an error occur when using Postfix virtual mailboxes?

Question

linux

Hello! In main.cf, I connected the configuration files for working with MySQL, now I see errors in the logs, and letters do not come to the mail.

postfix/virtual[16202]: fatal: bad string length 0 < 1: virtual_mailbox_base = 
postfix/master[15308]: warning: process /usr/lib/postfix/sbin/virtual pid 16095 exit status 1
 postfix/master[15308]: warning: /usr/lib/postfix/sbin/virtual: bad command startup -- throttling

I wrote the following lines in main.cf:

#Virtual domains, users, and aliases
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf,
        mysql:/etc/postfix/mysql-virtual-email2email.cf

I checked the requests in the files for correctness, everything is fine.

Answer 1

virtual_mailbox_base is not defined.