The Safe Limits
| Level | Limit | Notes |
|---|---|---|
| Per domain | 20-25/day | This is your real constraint |
| Per mailbox | 15-20/day | Stay conservative |
| Per tenant (Microsoft) | 10,000/day | Rarely the bottleneck |
Why These Numbers?
Email providers track sending patterns at the domain level. A domain suddenly sending 100+ emails/day is suspicious, regardless of how many mailboxes are used.
| Daily Volume | Provider Perception |
|---|---|
| 5-20 | Normal business |
| 20-50 | Active sales team |
| 50-100 | Potential automation |
| 100+ | Likely bulk sender |
Warmup Progression
| Warmup Stage | Emails/Domain/Day |
|---|---|
| Days 1-7 | 5-10 |
| Days 8-14 | 10-15 |
| Days 15-21 | 15-20 |
| Days 22-30 | 20-25 |
| Day 30+ | 20-25 (steady state) |
Scaling Volume Safely
Want to send more? Add domains, not mailboxes.
| Target Daily Volume | Domains Needed |
|---|---|
| 100 | 5 |
| 200 | 10 |
| 500 | 25 |
| 1,000 | 50 |
Time Distribution
Don't send all 20 emails at 9am. Spread throughout business hours:
| Time Window | Emails |
|---|---|
| 7-9 AM | 5 |
| 9-12 PM | 5 |
| 12-3 PM | 5 |
| 3-5 PM | 5 |
What Happens If You Exceed
| Severity | What Happens |
|---|---|
| Slight over (25-30) | Usually fine, monitor closely |
| Moderate over (30-50) | Throttling, delayed delivery |
| Significant over (50+) | Reputation damage, spam folder |
| Massive over (100+) | Domain may be flagged |
Key Takeaway
20 emails per domain per day is your safe limit. Want more volume? Add more domains. Spread sending throughout the day. Never burst large volumes from a single domain.