550 5.7.133 is a permanent SMTP reply meaning sender not authenticated for group (microsoft 365). This is a setting at the recipient's organization, not a problem with your domain. Microsoft says only the recipient organization's email administrator, or the group owner, can change it.
What 550 5.7.133 means
This is a setting at the recipient's organization, not a problem with your domain. Microsoft says only the recipient organization's email administrator, or the group owner, can change it.
Common causes
The group is internal only
Most commonDistribution lists and Microsoft 365 groups block outside senders by default.
You wrote to a team address
CommonAddresses such as sales@ or support@ are often groups with this setting.
The recipient's organization changed the setting
Less commonAn address that worked before now rejects outside mail.
How to fix 550 5.7.133
- 1
Contact the recipient another way
Ask them to allow external senders for the group, or to give you a direct address.
- 2
For the recipient's admin
In the Microsoft 365 admin center or Exchange admin center, allow external senders on that group or mailbox.
- 3
Nothing to fix on your domain
Your SPF, DKIM and DMARC are not the cause of this bounce.
Confirm your domain is set up correctly
Most delivery failures — permanent or temporary — trace back to authentication or reputation. Run a free EmailHealth check to confirm SPF, DKIM, DMARC, blacklist status, and TLS are all healthy for your sending domain. If you send in volume, free daily monitoring will alert you before a small issue becomes a flood of bounces.