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You can go to JEMHC > Messaging > Message Handlers and edit each to disable it (stopping inbound retrieval). Reverse process to re-enable.
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Outbound
You can go to JEMHC > Messaging > Message Outbounds and edit each to disable all mail sending (but events will still be captured, see next). Reverse process to re-enable.
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Webhook Event Capture (that drive notifications)
You can go to JEMHC > Notifications > Email and edit each to disable the Notification Mapping, this prevents JEMHC storing changes for the included Projects(s). Reverse process to re-enable.
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