I try to setup email filters in my email server to filter messages from zabbix and it isn't works normally. I detect that the problem is in email message headers.
When Zabbix sends message, the "From" header field contains text:
But when I send the message via some email client, it contains the space after ":" character:
and mail filter works normally.
Other header fields filled normally, with spaces after ":".
Please add the space after "From:" text in headers.