The correspondence with participants depends on a lots of factors. It is therefore quite hard to give a simple example of a recruitment email.
A concrete example:
If you take a look at page 54 (in chaper 5) in this online preview, you'll find an example of such an email. (From "Moderating Usability Tests" by Domas and Loring, (companion web site)).
Some additional information on the recruitment:
Recruiting participants is one of the most important phases you go trough when conduction usability tests. Without the right participants, the tests you perform can be a waste of time (or even worse - give you the wrong feedback).
"The Handbook of Usability Testing" by Rubin and Chisnell (companion web site) gives you a thoroughly walk-trough on the recruitment of participants. They have dedicated a whole chapter of their book to recruitment: Defining needs, characterizing user-groups/criteria, where to look for participants, the screening process, and follow-up.
You may be in touch with the potential participants 3-5 times:
- First an open advertisement or a direct invitation to a certain user-group.
- Then you send a confirmation to the participants that may fit your criteria, and ask them for a screening session.
- The screening is performed as an interview or as a questionnaire.
- Confirmation to the selected, best suited users.
- Follow-up and details due to the actual test session.
- Reminder (week before, day before).
- Debriefing and thanks after the session.
Now, when you have done some decisions on the requrements and recruitment process, the e-mail content is easier to produce. In your email, you may include something about:
- What the testing is and the purpose of the test.
- Requested information (job title, age, gender, phone etc). Don't include too much. Distinguish between contact information, rough selection and detailed screening.
- Compensation for participating in the test.
- Where and when.
- Attach some additional information, forms or questionnaires, like NDAs and pre-session questionnaire to avoid to much work on the testing day.
Remember: Don't reveal too much information. Don't mention client or product. The participants may look things up and "prepare" themselves for the test.
Keep it formal and simple, and most
important: Test the letter/email on other
people to avoid spelling
errors and ambiguous wording.