What outbound metrics should I track?

Track the metrics that map to revenue, not vanity. The core set: positive reply rate, meetings booked per 1,000 emails, reply-to-meeting conversion, show rate, and ultimately cost per booked meeting and cost per closed deal.

De-emphasise open rate (now unreliable) and raw emails sent (an activity metric, not an outcome). Review weekly: which messaging and segments produced qualified meetings, and double down on what converts rather than what gets opens.