Which node connects to email server?

Elastic Stack Elasticsearch
1

Hi, I have configured watcher email setting in elasticserach to send mails, currently i have 3 master nodes and 12 other nodes and all of them can reach the email server. The setup is working fine, now, I am planning to add more nodes to the stack, so should i add firewall rules to allow these nodes to reach the mail server as well?

or is it enough that if i just allow only the master nodes to reach the mail server?

2

The emails are sent from those nodes where the watches are executed. Execution happens on the master node on 5.x and on data nodes on 6.x and above (where the watcher shards are). If you are at least on version 6, all data nodes should be able to sent an email.