Set up an incoming mail trigger
Choose the mailbox whose incoming messages should start the run. You can narrow matching with a sender or subject filter, and use the unread-only option when the workflow should process only unread mail. The arriving message becomes the workflow input, including fields such as sender, subject, text, message identifier, and attachment details.
Design later steps around the fields the trigger supplies, and test the workflow with a representative message before relying on it. If a message has attachments, check how the mail step represents them and make sure downstream steps handle missing or unavailable files. Limit processing to the mailboxes and messages the workflow actually needs.
Prevent loops and duplicate handling
Only mail arriving in the selected mailbox starts this trigger. A message the account sends as a reply does not trigger it, which prevents a simple auto-reply from starting the same workflow again. If the workflow sends a reply, use the incoming message as the original input and avoid creating a second trigger for sent mail.
Consider what should happen when several messages arrive close together or the same message remains unread. Use the trigger's filters and any explicit workflow state checks to avoid processing messages outside the intended scope. Review the run history after the first live messages to confirm that the correct mailbox and fields were matched.