A visitor remembers you for about a day. Most teams send a single generic email a week later, by which point the conversation has merged with every other conversation that person had and the message reads as a mailshot, which it is.
Same day, from the person they met
A short message that evening, from the individual who had the conversation, naming the thing they talked about. Two sentences is enough. It is not a sales email, it is a bookmark, and its job is to make sure your name is attached to a real exchange rather than to a stand.
This is the message that decides whether the next one gets opened. Sent from a shared marketing address with a logo header, it does the opposite.
Within twenty-four hours, the personal one
The second message carries what you agreed to send. The specific thing, not a brochure: the comparable situation, the answer to the question they asked, the document they wanted. If you promised nothing, send the one thing that would have been useful to them given the problem they described.
It should end with the next step and a date, phrased as a question with two options. Open-ended availability questions produce silence, because answering them is work.
Day three, the decision point
If there is no reply by day three, send the short one that makes no easy: the diary is filling, the month after is just as good, which suits. That converts a dead thread into a dated one more often than another chase does.
After that, the contact moves to a normal sequence rather than an event one. Continuing to reference the show after the first week is a reminder that they have not replied, which is not the reminder you want.
Grade A and B differently
A grades get the three messages above, individually written. B grades get the same first message and then a lighter sequence, because the thing missing was timing and the job is to be present when the timing arrives rather than to push now.
C grades get a newsletter or nothing. Treating a badge scan to a personal follow-up wastes the time that should have gone on the A list, and it is usually why the A list gets followed up late.