Can a workflow write a different AI email for each contact?

Yes. In the workflow's Email step you can have AI generate the email on the fly, custom to each person. Write instructions such as: write a message to this customer to get them an appointment to discuss their website. Then insert custom fields for the data you have on them, for example website, SEO score, industry and whether they advertise. Because the variables are inserted, each email is different.

You can choose whether to include the agent's system prompt. If it is included, the agent's main prompt is used as well; otherwise only these instructions are used.