There is a function call:

$formatted_domain = substr_replace($domain, '-', strrpos($domain, '.'), 1);

which does replacement only for 1st match of a dot
https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/ui/app/controllers/CControllerMediatypeUpdate.php#129
which, when I use email as "[email protected]"  results SMTP server name auto-parsed as:

SMTP server: "this.is-domain.mail.protection.outlook.com"

while it must be :

SMTP server: "this-is-domain.mail.protection.outlook.com"

This should be fixed to replace all "." entries in the domain name, not only one 1st found.