550: the recipient blocked you personally
A person at the recipient company, or their administrator, added your address or domain to their own blocked senders list in Mimecast, so your mail is refused.
- Mimecast
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550
- Provider
- Mimecast
- 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 recipient's side. Their mail admin has to change something; you can tell them.
- What the server says
550 Envelope blocked – User Entry.
What it means
Mimecast lets users manage their own senders, and blocking someone there creates a personal block entry. This reply means your address (User Entry) or your whole domain (User Domain Entry) is on such a list for the recipient, and Mimecast rejects the message permanently. It is a decision made for that mailbox, not a judgment of your server or reputation, so other people at the same company may still receive your mail. Mimecast’s fix is to remove the entry from the Managed Senders list, which the recipient or their administrator has to do.
Common causes
- The recipient clicked block on one of your earlier messages.
- The recipient blocked your whole domain rather than one address.
- An administrator added the block on the recipient’s behalf.
How to fix it
- 01Stop sending to this address; repeated attempts will not get through and can harm how others treat your mail.
- 02If the contact is wanted, ask the person through another channel to remove you from their blocked senders.
- 03Their administrator can also remove the entry from the Managed Senders list in Mimecast.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Policies - Mimecast SMTP Error Codes (Mimecast support)mimecastsupport.zendesk.com
Related codes
- 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.
- 550Blocked by the company’s Blocked Senders policy.An administrator of the recipient’s Mimecast account set a Blocked Senders policy that matches your From or envelope sender address, so the message is refused.
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.
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