Sending.ac Review 2026: Azure/Entra Cold Email Infrastructure

By Puzzle Inbox Team · May 7, 2026 · 6 min read

Sending.ac offers Azure cold email infrastructure with up to 150 mailboxes per domain. This review covers the high-density approach for cold email.

Sending.ac Review: High-Density Azure Cold Email

Sending.ac uses Microsoft Azure infrastructure to provision up to 150 mailboxes per domain — much higher density than standard MS365 (5-10 per tenant) or GWS (3 per domain). For cold email operations needing high mailbox density within limited domain counts, Sending.ac is the specialized choice.

What Sending.ac Offers

• Azure/Entra tenant-based infrastructure
• Up to 150 mailboxes per domain
• Microsoft cloud reputation inheritance
• Dedicated tenant isolation

Sending.ac Pricing

Per-tenant or high-density pricing model. Favorable unit economics at high mailbox density.

The High-Density Value Proposition

150 mailboxes per domain means fewer domains to purchase and manage. For cold email operations running volume campaigns from limited domain sets, density matters.

The Deliverability Trade-offs

High-density sending patterns can trigger Microsoft anti-abuse systems faster than standard MS365. Balance between density advantage and detection risk.

Who Sending.ac Is Good For

• High-volume cold email operations with Microsoft-heavy ICP
• Teams optimizing for density (mailboxes per domain)
• Operations accepting Azure/Entra vs standard MS365 trade-offs

Who Should Look Elsewhere

• Standard cold email operations (MS365 fits better)
• Teams prioritizing long-term account stability over density