When adding a custom field in service desk (Setup > Custom Fields > Incident) there is no option to add the custom field to an email template (Setup > Email > Templates). Users creating incidents through emails can add additional information to the email to populate required custom fields
While sending the email, custom fields can be added but it's not possible while pursing the emails. New functionality to be added to support that. Will take a call during 8.x
While sending the email, custom fields can be added but it's not possible while pursing the emails. New functionality to be added to support that. Will take a call during 8.x