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Go to Jira Administration > Add-ons> Electronic Signature Fields > Configuration.
Set up your Username check sensitivity and Maximum invalid login attempts.
Info This feature is available starting with version 2.0.1 for Jira 8 and above.
Set up the Email subject and Email body that will be sent once the signature from specific approvers will be the specific user(s) or group is requested. For more details please see ESF validator.
Info This feature is available starting with version 3.0.0 for Jira 8 and above.
Status colour Yellow title in progress 
That's it. Electronic Signature Fields are now set up.
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