How do I warm up a dedicated IP for a 40,000-email marketing send in two days?

Hi! With a brand-new dedicated IP, pushing 40,000 marketing emails in ~2 days is one of the riskiest things you can do for deliverability—if mailbox providers see a sudden “cold IP + high volume” spike, you’re much more likely to get throttled, junk-foldered, or rack up complaints that hurt both the IP and the client’s domain reputation. The safest play is to either (a) use a reputable shared IP / shared pool for this one-time campaign, or (b) extend the ramp (even to just 7–14 days) and send your most engaged recipients first.

If you can change the setup (best option for a one-off)

• Use a shared IP (or the ESP’s warmed “shared marketing” pool) for this campaign instead of a dedicated IP. Dedicated IPs are best when you have consistent volume every week/month; a one-time blast doesn’t “stay warm,” so you take on risk without much long-term benefit.
• If the client insists on separation, consider sending marketing from a subdomain (e.g., news.clientdomain.com) so any reputation bumps are less likely to spill over to their primary domain used for 1:1 or transactional mail. (Still authenticate it with SPF/DKIM/DMARC.)

If you must use the dedicated IP, adjust the send schedule (safer warm-up approach)
To warm up, you want predictable volume increases and high engagement early. That usually means you should not try to finish in 2 days.

A practical ramp for 40,000 total (example)

• Day 1: 500–1,000 (most engaged: recent openers/clickers, recent signups)
• Day 2: 1,500–2,500
• Day 3: 4,000–6,000
• Day 4: 8,000–10,000
• Day 5: 12,000–15,000
• Day 6–7: send the remainder (only if metrics are clean)

If you see throttling/deferrals, elevated bounces, or complaints, hold the volume steady (or drop it) for a day rather than continuing to scale.

Make the warm-up “friendly” to mailbox providers
A few things matter a lot more than people expect during a first send:

• Segmentation first: Start with recipients most likely to engage. Don’t include cold/old addresses early.
• List hygiene: Remove role accounts (info@, support@), hard bounces, and long-term non-openers from the first waves. For a one-time campaign, it’s often smarter to not mail the stalest portion at all.
• Compliance signals (now table-stakes): Make sure SPF, DKIM, and DMARC pass, and include one-click unsubscribe (List-Unsubscribe headers + a visible unsubscribe link). Also honor unsubscribes quickly (many providers expect within ~48 hours).
• Consistent identity: Keep the same From name/address and avoid big creative swings between warm-up batches.
• Watch the right metrics: Complaint rate and bounce rate are your “stop/go” signals. If either spikes, slow down immediately.

If the business requirement is truly “all 40,000 in 2 days”
Then the least-bad compromise is:

1. Use a shared/warmed sending pool (recommended), or
2. Send only the top engaged segment in those 2 days (for example, the best 10k–20k), and schedule the rest over the following week, or
3. Split the send: keep the dedicated IP volume modest and move the remainder through a warmed path (shared pool or an already-established sender) to avoid a single cold-IP surge.

If you tell me roughly what % of the list has opened/clicked in the last 30–90 days (and whether the client has sent marketing from this domain before), I can suggest a tighter ramp and segmentation plan that fits your timeline with the lowest realistic risk.