# SMTP: 550 5.4.1 Recipient address rejected: Access denied. AS(201806281) [DB5EUR03FT015.eop-EUR03.prod.protection.outlook.com]

**Code:** `550 5.4.1 Recipient address rejected: Access denied` · **Category:** Email / SMTP · **Seen on:** SMTP

Microsoft 365 / Exchange Online rejected the message because the recipient address does not exist in that tenant (Directory Based Edge Blocking).

## Meaning

Since 2018 Exchange Online rejects mail for unknown recipients at the edge. The address is misspelled, deleted, not yet synced from on-premises Active Directory, or the mail flow connector is wrong. Ask the recipient for the correct address, or fix the sync.

## Common causes

- Typo or non-existent recipient address
- User deleted or never licensed in Microsoft 365
- Hybrid sync (Azure AD Connect) not yet replicated the mailbox
- Accepted domain set to Internal Relay without a connector
- Distribution group restricted to internal senders

## Quick fix

1. Verify the exact address with the recipient
2. Admins: confirm the mailbox exists in the Microsoft 365 admin centre
3. Check accepted domain type (Authoritative vs Internal Relay)

## Detailed fix by platform

### PowerShell

1. `Get-Recipient user@contoso.com` in Exchange Online PowerShell confirms whether the address exists

## How to diagnose

1. **Address** — Spelled correctly?
2. **Tenant** — Mailbox exists and is licensed?
3. **Sync** — Hybrid/AD sync complete?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/email/550-5-4-1-recipient-address-rejected-access-denied)