The simple thank-you
Use when: You had a good conversation and want to stay in touch, with no specific ask yet.
Subject: Great meeting you at [event name]
Hi [first name], It was great meeting you at [event name] last night. I enjoyed hearing about [specific detail, e.g. how your team is rebuilding onboarding]. I would like to stay in touch. If anything comes up where I can help with [your area], just say the word. Best, [Your name]