Use a memory that identifies the relationship
Mention a class, house, club, trip, or ordinary ritual you genuinely remember. Explain what brought them to mind instead of opening with a generic networking phrase.
Meet the person they are now
Offer a brief life update and ask an open question without demanding a complete account of the missing years. Avoid assuming their career, family, health, or identity stayed the same.
Offer a small next step
Suggest a short call, coffee when nearby, or simply exchanging updates. Let a warm reply remain a warm reply instead of pushing immediately for restored best-friend status.