550: blocked by a content rule
Something in your message matched a content rule the recipient company set in Mimecast, such as a word, phrase or attachment type, and the message was 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
- Either side, depending on the cause. Start with the checks below that are yours.
- What the server says
550 Message bounced due to Content Examination Policy.
What it means
Mimecast customers can write Content Examination policies that look inside messages for words, phrases or other content they do not want to receive, and act on a match. This reply means one of those rules matched and its action was to bounce the message. The rule belongs to the recipient company, so its exact contents are not public and the bounce will not say which part matched. The rejection is permanent for that message. Changing the content can get the next one through, and Mimecast’s documented fix is a bypass or an adjustment of the policy by the customer’s administrator.
Common causes
- A word or phrase in the subject or body matches a rule the company wrote.
- An attachment, file type or link matches a rule.
- A signature, disclaimer or tracking element added by your sending tool matches a rule.
How to fix it
- 01Compare the rejected message with ones that got through to see what was different.
- 02Resend a plainer version without attachments, unusual links or tracking.
- 03If the content is needed, ask the recipient to have their IT team add a Content Examination bypass or adjust the policy.
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
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.
All 19 Mimecast codesEvery code in the wikiPaste your own bounce