5.7.606: Banned sending IP (Microsoft)
At a glance
- Type: permanent failure (class 5, RFC 3463 §2). The sending server does not retry; sending the same message again fails the same way until the cause is fixed.
- Basic code: varies; the enhanced code is the part that identifies the problem.
- Enhanced code 5.7.606: not in the IANA registry; the group is security or policy status (RFC 3463 §3.8).
- Who uses it: Microsoft: access denied, banned sending IP (5.7.606 to 5.7.649).
A 5.7.606 bounce from Microsoft means Microsoft has banned the IP address your mail came from. Every message from that IP to Microsoft-hosted mailboxes will be refused until the IP is delisted.
What it means
These are Microsoft's codes, not ones from the IANA registry. Microsoft's Exchange Online NDR reference uses the whole range from 5.7.606 to 5.7.649 for access denied because the sending IP is banned. A separate code, 5.7.511, is also a banned sender IP but has its own delisting route (below).
The ban is on the IP address, not on your domain or your account. If you send through a service that shares IPs between many customers, another customer's mail may be the reason.
Common causes
- Spam or bulk mail to addresses that never asked for it went out from that IP.
- A compromised account, website form or server on that IP sent spam.
- Many messages went to addresses that do not exist, a sign of an old or bought list.
- The IP is new, or was recently reassigned, and inherited a bad history.
- A shared IP pool was used by another sender with poor practices.
How to fix it
- Find the sending IP in the bounce. If it belongs to your email service, contact the service first and ask it to handle the delisting or move you to a different IP.
- Stop the cause before you ask for delisting: secure compromised accounts and forms, stop sending to lists you cannot vouch for, and remove addresses that bounce.
- Check SPF, DKIM and DMARC (SPF checker, DKIM checker, DMARC checker).
- Microsoft asks senders to follow good deliverability practices and then to submit the IP through its delist portal,
sender.office.com, as described in the NDR reference. - For 5.7.511, Microsoft's route is to email
delist@microsoft.comwith the full bounce message and the IP address. - Once delisted, raise volume gradually and keep watching bounces and complaints.
What to do with the address
Keep it for now; the ban says nothing about this mailbox. But if bad addresses on your list helped cause the ban, clean the list before you resume. Bulk email verification can check a list before you send again. For other Microsoft blocks, see 5.7.708 for tenant-wide restrictions and 550 5.7.1 for general policy refusals.
Related codes
- 550 5.7.1: Delivery not authorized: refused for policy reasons
- 5.7.708: Tenant traffic not accepted from this IP (Microsoft 365)
- 421 4.7.28: Unusual sending rate or unsolicited mail: rate limited
See every bounce code in the dictionary.
Many bounces from addresses that do not exist can be avoided: check an address with our free email checker, or clean a whole list before you send.
How we wrote this: drafted by the email-validation.org team with the help of AI writing tools, from our product documentation and the sources linked in the text.