Email to Purchase request

Email to Purchase request

We have some email template that users can complete and send into the servicedesk, How do I get SDP to recognise this type of email as a service catalogue type rather than an incident? As its an incident I don't have the option to create a New Purchase request from the ticket. I have looked at business rules but cant see anything that works.
If I look at the incident and under actions if I use the option "convert to service" it then gives me this PR option but I would like to have this applied automatically based on the subject of the call being a certain phrase.

Any ideas if this is possible or how to do it?

Thanks

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