TenantCore Notes

Practical notes for people who run outbound infrastructure.

Notes on domains, mailboxes, DNS, sending limits, monitoring, and outbound operations.

Featured

Infrastructure · 6 min read

Why Microsoft 365 Cold Email Inboxes Keep Breaking (And How to Fix the Infrastructure)

When cold email inboxes stop performing, operators often blame the sending tool. The real problem is usually the Microsoft 365 infrastructure underneath them.

Apr 23, 2026

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All notes

Setup Guide

How to Set Up Microsoft 365 Domains and Inboxes for Cold Email in 2026

A step-by-step guide to structuring Microsoft 365 tenants, domains, mailboxes, and cold email inboxes for sustainable outbound operations.

Apr 23, 2026

Technical

Cold Email Inbox Send Limits: Exchange Enforcement vs. Sending-Tool Settings

Why daily inbox and mailbox limits inside a sending tool are not enough, and what changes when Exchange enforces the limit underneath every sending tool.

Apr 23, 2026