Error:
The MySQL client (libmysql.dll, 32 bit) could not be loaded.
hMailServer needs this file to be able to connect to MySQL.
The MySQL client needs to be manually copied to the hMailServer Bin directory. The file is not included in the hMailServer installation.
Path: C:\Program Files (x86)\hMailServer\Bin\libmysql.dll
It's a bit more complicated. You should read this Article which explain why it can be problematic with hMailServer 5.6.x and MySQL 8.x or higher
Support article: https://www.hmailserver.com/forum/viewtopic.php?f=10&t=33531
MySQL-Archive Downloads for MySQL 5.x compatible libmysql.dll versions https://downloads.mysql.com/archives/community/