Microsoft issues
Outlook.com and Microsoft 365 delivery problems — junk, throttling, or blocking.
- Reading time:
- 5 min
- Difficulty:
- Intermediate
- Estimated duration:
- 5 min
- Prerequisites:
- None
- Last updated:
- 2026-07-15
- Author:
- empire
Problem summary
Outlook.com and Microsoft 365 delivery problems — junk, throttling, or blocking.
Severity: High
Symptoms
- Microsoft destinations junk or reject disproportionately
- SNDS filter scores degrade
- SmartScreen / junk rules hit corporate tenants
Possible causes
- IP reputation as seen by Microsoft
- Complaint or trap activity
- Tenant-side policies beyond sender control
How to diagnose
- Inspect SNDS and JMRP/FBL where available
- Differentiate consumer Outlook.com vs Microsoft 365 tenants
- Validate authentication on Microsoft samples
How to fix
- Remediate sending IPs and reduce complaints
- Align with Microsoft sender guidelines
- Work with recipient admins when tenant policies block mail
How to verify
- SNDS improves and junk rates fall
- Microsoft cohorts deliver consistently
Prevention
- Monitor SNDS
- Keep complaint rates low
When to escalate
- Production mail is failing for a material share of recipients after remediation attempts
Related Problems
- Apple Mail issuesProblems observed primarily in Apple Mail / iCloud paths — filtering, privacy-driven open noise, or junking.
- Gmail issuesBroad Gmail delivery or placement problems spanning Postmaster signals, spam, and throttling.
- Yahoo issuesYahoo and AOL delivery or spam-folder problems concentrated at those providers.