Hi Yolanda,
Since you already have email alerting configured, you can add these specific rules to your ossec.conf on the manager:
<email_alerts>
<email_to>your-emaiil-here</email_to>
<rule_id>5715</rule_id>
<do_not_delay />
</email_alerts>
where:
Rule 5715 - Agent disconnected
Rule 5716 - Agent reconnected
you can find more rules here:
https://github.com/wazuh/wazuh/blob/master/ruleset/rules/0016-wazuh_rules.xml