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e.g. add two transitions called "Approve" and "Unapprove" to a status you like e.g. "Approval in progress".

Configure Field Rules

Field Contexts and Field Rules allow you to manipulate issues and issue fields based on email content.

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1. Add a Field Rule with the following attributes:
   1. Goal: Execute workflow transition
   2. Regular Expression: (?i)Decision: (.*)
   3. Match in: Email Subject
   4. Value from: Capture Group 1
   5. Order: 1
2. Optionally you may want to store the approvers / unapprovers who already replied in a multi user picker field, to do this add a field rule:
   1. Goal: Set Fields in Existing Issues
   2. Regular Expression: .*
   3. Match in: Sender Email Address
   4. Value from: Capture Group : whole expression
   5. Issue Field: select a multi user picker field, e.g. something called "Already Replied"
   6. Order: 1

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