There are three places that can affect automatic Zoom emails for sessions created through HeySummit.
HeySummit's Zoom host setting: In HeySummit, go to Event Settings > Integrations & Developer > External Webinar Accounts, open the host's Actions > Zoom Settings, or Actions > Edit Host where that label is shown, and use Ask Zoom to send registration confirmation emails?. This is an event-wide setting and requires access to manage the host. By default, HeySummit keeps it off, which means HeySummit asks Zoom not to send registrant confirmation emails when attendees are registered with Zoom.
Zoom account-level webinar email settings: This is usually the best place to disable Zoom's own automatic webinar emails globally, and review the settings on each affected webinar as well. Account policies and webinar-specific settings can affect which changes are available.
Individual Zoom webinar settings: Use this only when a specific webinar needs different email behavior, because you may need to adjust it again after HeySummit creates or updates the webinar.
For the Zoom account-level settings, open Zoom and go to Account Management > Account Settings > Webinar > Emails. You must have permission to edit those account settings. Turn off the automatic emails you do not want Zoom to send, including any relevant reminders and follow-ups. HeySummit's confirmation-email toggle does not switch off every Zoom email.
If you prefer to change email behavior for one webinar only, open that webinar in Zoom and adjust its email settings directly. This can be useful for exceptions, but it is more manual because each newly created webinar may need to be checked.
For most HeySummit events, keep Zoom's automatic registrant emails off and use HeySummit's attendee emails instead, so attendees receive one clear set of event communications. See Zoom's webinar email settings guide for current account-level and individual-webinar controls.