Action Email user - (requester and CCs) is never suppressed when someone is making a ticket update via Help Center channel.

Email suppression rules only apply to a trigger when the requester/CC uses Reply All via Email channel.

Key Points from Zendesk Documentation

Trigger conditions and actions reference

There's a known limitation for using the Email user + (requester and CCs) action and the Ticket + is + Updated conditions in triggers. When used together, Support suppresses emails to a user if the ticket update is from that same user. This is expected behavior to eliminate redundant emails.

Understanding suppression of CCs email notifications

The Email user + (requester and CCs) action is also suppressed when the ticket is being updated (not created) ****via email**** <--- this is the key point

To address one of Rudy's original questions, "...when requester updates his own ticket, is there a way to notify requester/CC only if ticket has 1 or more CC?"

I think this is possible but would just be a bit involved. Something like this might work:

1. On ticket update, via webhook to Zendesk API, conditionally update ticket with a tag using liquid if CCs list has >1 name

"additional_tags": "
{% if ticket.ccs.size > 1 %}has_multiple_ccs{% endif %}
"

2. Have separate "notify requester/ccs" triggers. If tag is present, notify everyone/including requester. If tag isn't present, only notify requester