Anyone can send an email to Service Desk Plus, and this means creating login accounts for dozens of people!

On the other hand, it is not possible to filter everyone as spam because the sender's email address is unpredictable.

This is big problem! I Suggest a good idea:

Login account creation confirmation, when an email receiving.

For example, if someone sends an e-mail to Service Desk Plus, the administrator will first approve him. If his request is approved, his request will be registered in Service Desk Plus and his Self-service login information will be sent to him/her.