This is an example of an invitation mail text. Feel free to adapt it to your needs:
> Hello everyone,
>
> I would like to invite you to participate in an upcoming user study for my {+ bachelor's/master’s/doctoral thesis +} exploring {+ topic X+}.
>
> The study will take place from {+ month, start day +} to {+ month, end day +} in the VR Lab located at Kopernikusstraße 6. You will be picked up at the entrance door of the building. Each session will take around {+ X +} minutes to complete.
>
> The time slots for the study can be found in the {+ Foodle/Doodle +} link: {+ Insert link here +}
> For our convenience, please cast your vote to the earliest available timeslots possible, and don't forget to hit the submit button on the very far right of the page (horizontal scrolling required).
>
> The pre-requisites for participation are simple:
> - Fluently speaking and understanding English
> - Normal depths vision
> - Not being color blind
> - Being able to stand for up to {+ Y +} minutes
> - …
>
> I am looking forward to seeing you during my study and greatly appreciate your support!
