4 follow-ups isn't unreasonable on its own — deliverability harm comes more from how recipients respond (spam complaints, low engagement) than from the raw follow-up count. The bigger risk is continuing to email people who've shown zero engagement across the whole sequence (no opens, no clicks, no replies) — that pattern of continuing to email someone who's clearly not interested is what tends to generate complaints and hurt sender reputation over time. A good practice: if someone hasn't engaged at all by follow-up 2 or 3, consider that a signal to stop rather than pushing through all 4 regardless.