550 5.1.8: Bad outbound sender: account blocked from sending
Microsoft 365 has blocked this account from sending email, usually because it sent spam, often after being hacked.
Blocked The address is probably fine. The problem is how the mail was sent.
What the bounce message looks like
The wording changes from one provider to another. These are typical examples:
550 5.1.8 Access denied, bad outbound senderCommon causes
- A compromised account that sent spam
- Sending more than the outbound limits allow
How to fix it if you sent the email
- Change your password and turn on two-step sign-in right away.
- Tell your IT admin; they have to unblock the account.
If you manage the receiving or sending mail system
- Secure the account, then remove it from the Restricted entities page in Microsoft Defender.
Free tool: paste the full bounce into the bounce message decoder to get a plain-English reading of every code in it.
Questions people ask
- What does 550 5.1.8 mean?
- Microsoft 365 has blocked this account from sending email, usually because it sent spam, often after being hacked.
- Is 550 5.1.8 a hard or soft bounce?
- Blocked. The address is probably fine. The problem is how the mail was sent.
- Should I remove the address after a 5.1.8 bounce?
- No. Fix how the mail is sent; the address itself is probably fine.