Another approach you might find useful is by splitting your list and segmenting your most valuable customers and focus on them first.
I've done lots of 30/60/90 day period inactive campaigns because that's what I was previously told to do, but now, mapping out how long on average that segment stays with you before going inactive and including a specific value prop or benefit reminder in a three part win-back series, the comparison is unbelievable. I also use that timeframe to produce a trigger that happens a couple of weeks previous so I can email recipients before they hit that inactive period and target them. Keeps retention high and I’m a firm believer in looking after existing customers rather than always trying to prospect.
If you’ve got a large section of your list which have never purchased and they’ve been on your list for years, why spend the effort and resource to try and keep them when they’re actually costing you money?