Start with the warmest
Segment quiet enquiries by recency and intent. Someone who asked about fees last month is a better start than someone who downloaded a brochure last year.
Lead with something new
A new batch, a seasonal offer, or a relevant review gives people a reason to reply that is not 'just checking in'.
Stop when they say stop
Three touches over two weeks is plenty. Respect opt-outs and log every outcome so the next campaign gets smarter.