Infrastructure Blueprint
1. ESP Mix Strategy
Enterprise / Finance Lists
70% Google 30% Microsoft
SMB / E-com Lists
70% Microsoft 30% Google
2. Domain & Warm-Up Rules
- Register domains >30 days before sending. Verify with Google Postmaster Tools.
- Gmail Targets: Run warm-up forever at 1.3-2x cold volume.
- Outlook Targets: Warm-up optional unless also sending to Gmail.
- Avoid warm-up spikes; they trigger tenant blocks immediately. (See Microsoft Sender Support).
Core Deliverability Levers
| Lever | Google Workspace | Microsoft 365 / Outlook | The Operator's Play |
|---|---|---|---|
| Reputation Signal | Domain age & engagement | IP-pool health & LLM filters | Buy aged domains for Google; secure clean IP ranges for Microsoft. |
| Copy Sensitivity | Moderate | Extreme (LLM Scans) | Outlook needs <40 words. No greeting. No signature. One question. |
| Volume / Mailbox | 20-50 / day | 2-5 / day (max 40) | Watch your B2B complaint ratio like a hawk. |
| Key Error Codes | "High Spam Rate" | 550 5.7.708 ("Bad IP") | If 5.7.708 appears, move pools via support immediately. |
Copy & Campaign Framework
Outlook Strategy (LLM Era)
Strict filters. Minimalist approach.
Subject Line:1-3 plain words. No emojis. Lowercase.
Body Copy:15-40 words max. 1 sentence + 1 question.
"Alex — saw you use Stripe. Refunds still a nightmare?"
Signature:First name only. No title, phone, or logo.
Gmail Strategy (Mixed Lists)
Standard filters. Value-first approach.
Subject Line:Same as Outlook, but light spintax allowed.
Body Copy:40-90 words. Personalized opener → Value Line → Soft CTA.
Opt-Out:Avoid "unsubscribe". Use "Let me know and I'll drop this."
The Daily Operational Checklist
Map target inbox split (70/30 rule)
Pre-buy domains & age them 30 days
Create one tenant per 1-2 Outlook domains
Start Gmail warm-up at 1.5x volume
Write <40-word Outlook templates
Monitor daily logs; swap inboxes if bounce >3%
Review EmailGuard weekly (flag <8/10)
Test new copy before blaming infrastructure