Since Upgrade to 1.8.3 SMTP-Check perodically failed. At least 1-2 times per hour ZABBIX reported that the SMTP-Server ist Up. The remaining period ZABBIX reported the SMTP-Server as down.
But the SMTP-Server works fine, also while ZABBIX is reporting them down.
Probably closed Issue
ZBX-2926 is the same Bug?