550: not an Xfinity customer
The address you sent to does not belong to an Xfinity customer. The failure is permanent, and Xfinity asks bulk mailers to treat it as an unsubscribe.
- Comcast
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550
- Provider
- Comcast (Xfinity)
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
550 Not our customer
What it means
Xfinity returns this 550 when a message is sent to an Xfinity customer that does not exist, so there is no mailbox to deliver to. The failure is permanent. Xfinity asks bulk mailers to treat the reply as an unsubscribe and stop mailing the address. An address that worked in the past may have been closed since, which is one way an old list fills up with them. Sending again and again to addresses that do not exist also tells receivers that a list is not maintained.
Common causes
- The address was mistyped.
- The account was closed or never existed.
- The address came from an old or bought list.
How to fix it
- 01Do not retry the message.
- 02Remove the address from your list and suppress it, as Xfinity asks of bulk mailers.
- 03Confirm the correct address with the recipient another way.
- 04Use confirmed opt-in and remove hard bounces after every send.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 550Account not available.The Xfinity account you wrote to is currently not available. Xfinity sends this as a 550, so the message has failed, though the account itself may come back.
- 550Too many invalid recipients.Xfinity refused the whole message because too many of its recipients were invalid, so nobody received it. Clean the recipient list and send it again.
- 550Mailbox unavailable.The receiving server permanently refused the message for this recipient: the mailbox does not exist, cannot be reached, or the server rejected the message by policy.
550 at other providers
- 550 [SC-001]Outlook.com policy block for content or reputation.Outlook.com rejected the mail for policy reasons tied to spam-like content or to the reputation of the sending IP or domain.
- 550 [SC-002]Outlook.com block for namespace mining.Outlook.com blocked the sending IP because it behaved like a namespace miner, checking whether addresses exist without sending mail.
- 550 [SC-003]Outlook.com block for an open proxy or relay.Outlook.com rejected the mail because the sending IP appears to be an open proxy or open relay.
- 550 [SC-004]Outlook.com block after complaints.Outlook.com placed a block on the sending IP because it received complaints about mail coming from it.
- 550 [DY-001]Outlook.com refuses dynamic IP addresses.Outlook.com rejected the mail because the sending IP is dynamic address space, which it generally does not accept mail from.
- 550 [DY-002]Outlook.com block for a likely compromised sender.Outlook.com rejected the mail because the sending server or computer appears to be compromised or infected.
Further reading
All 33 Comcast codesEvery code in the wikiPaste your own bounce