Messages stuck in the outbox. Emails bouncing back. Recipients saying they never got it. Microsoft 365 mail flow problems stop your business cold — we diagnose the root cause and fix it fast, usually the same day you call.
These are the exact symptoms businesses call us about every week. If even one matches, we can help.
Emails stuck in Outbox
Messages that never leave — no bounce, no delivery, just sitting there.
NDR / bounce-back errors
"550 5.1.1 User unknown" or similar non-delivery reports from Microsoft.
Recipient says email never arrived
You sent it, you can see it in Sent — they swear it's not there.
Email works for some, not others
Certain domains or contacts consistently fail while others work fine.
Email sending too slowly
Messages arrive hours late or in batches — throttling or connector issue.
External contacts marked as spam
Your outbound email lands in junk or is blocked outright by recipient servers.
Microsoft 365 mail flow failures have specific, diagnosable causes. We identify the exact layer — DNS, connector, license, or policy — in the first 15 minutes of investigation.
MX, SPF, DKIM, or DMARC records that are wrong, expired, or pointing at the old mail server will cause sending failures and rejections.
Connectors in Exchange Admin Center with wrong smart host settings, certificate mismatches, or TLS enforcement issues commonly cause outbound failures.
An expired, unassigned, or downgraded license can silently disable a mailbox — the user can log in but mail stops flowing.
Microsoft automatically restricts accounts suspected of sending spam. If one account was compromised, it can affect the whole tenant's outbound reputation.
The problem isn't Microsoft — it's the receiving server. Your IP or domain is on a blocklist, and messages are rejected before they arrive.
Security gateways (Mimecast, Proofpoint, Barracuda) misconfigured during setup or after an MX change route mail incorrectly or drop it entirely.
A structured diagnosis — not trial-and-error — means faster resolution with no side effects.
Message trace analysis
We pull the Microsoft 365 Message Trace for affected messages to see exactly where delivery failed and what error code was returned.
DNS record audit
We check MX, SPF, DKIM, and DMARC records against your current Microsoft 365 tenant configuration. A single misaligned record breaks deliverability.
Connector & transport rule review
We audit Exchange Admin Center for misconfigured mail flow rules, connector settings, and any tenant-level blocks placed by Microsoft.
License and mailbox status check
We verify license assignment, mailbox health, and account status — a single expired license or disabled account is easy to miss.
Sender reputation review
We check your domain and IP against major blocklists and review Microsoft Secure Score for outbound reputation issues that cause rejections.
Fix, test, confirm
We apply the fix, send a live test, and confirm delivery end-to-end — then walk you through what changed and how to prevent recurrence.
While we're in your tenant, we often resolve related issues that were quietly causing problems in the background.
We support Microsoft 365 for businesses throughout Maryland. Most mail flow issues are diagnosed and resolved in a single session.
