Can I change the requester based on the email body

Not with a trigger. But Zendesk has agent forwarding, which sets the original sender as the requester, and it has four conditions.

Not with a trigger. A trigger can test whether text contains something, but it cannot lift a value out of a message and use it as a field. What does solve this is agent forwarding: forward an email and the ticket is created with the original sender as the requester.

How do I set the requester from what is in the email?

• Enable email forwarding has to be on, on the Agents settings page.
• The person forwarding must be an agent or admin. A forward from anybody else does not qualify.
• The subject must contain fw, fwd or the equivalent in another language.
• In the body, the text From: and the requester's email address must sit on the same line.

That last one is why it works for some colleagues and not others: Zendesk only reads the From field in the body of the forwarded message, and mail clients lay that block out differently. Test with the client your team uses rather than assuming.

When it still does not apply

Agents can change the requester by hand, which is two clicks and the honest answer for occasional forwards. Beyond that, an integration can read the body and set the requester through the API, but that is real work and only pays at volume.

The better fix is usually upstream. If a colleague forwards regularly, either the customer should be writing to your support address, or that colleague should be raising the ticket properly. And when an agent does correct a forwarded ticket, CC the person who forwarded it: they stay informed, and they learn what happened without being told off.

See also

• Changing the requester of a ticket
• Forwarding email from your own address