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Mimecast 550 Envelope blocked: sender on a block list

550 Envelope blockedMimecast blocked sender entryPermanent: retrying will not helpFrom Mimecast

Example
550 Envelope blocked - User Entry

What it means

An “Envelope blocked” reply means Mimecast matched your envelope sender against a block list held by the recipient organization and refused the message. No content check is involved; the decision is about who you are.

The suffix tells you who created the block. “User Entry” and “User Domain Entry” point to a personal block made by an individual user, typically from Mimecast’s end-user tools when they blocked a sender or a whole domain. “Policy Entry” points to a block the organization’s administrators set in a blocked senders policy. The exact suffixes can differ slightly between versions, so read what your bounce says.

It is a permanent 550. Retrying or changing the subject will not get through. Because the block is a deliberate choice made by someone at the recipient, the only real route is to ask them, through another channel, to review it.

Likely causes

  • The recipient clicked block on one of your earlier messages, perhaps by mistake while clearing spam.
  • An administrator added your domain to a blocked senders policy after a phishing wave that spoofed it.
  • Your domain shares a name pattern with a blocked domain, and the admin blocked a wide pattern.
  • You send newsletters the recipient no longer wanted and they blocked rather than unsubscribed.

How to fix it

  1. Check which suffix your bounce shows, so you can tell the recipient whether the block is personal or organizational.
  2. Contact the person by phone or another email account and ask them to remove you from their blocked senders.
  3. For a Policy Entry, ask them to pass the bounce to their IT team, who can remove the entry in the Mimecast console.
  4. If your domain was blocked because it was spoofed, publish a DMARC policy at quarantine or reject so the admin can trust authenticated mail from you again.

Checks that apply

  • DMARC Check Shows whether your domain has an enforcing DMARC policy, a strong argument when you ask an admin to unblock it.
  • MX Lookup Confirms the recipient’s MX belongs to Mimecast, so you know the block sits there and not at another filter.
See the example diagnosed

The classification runs without network lookups and we never store your paste.

FAQ

Can I tell who blocked me?
Only roughly. A User Entry suffix means one person at the recipient did it; a Policy Entry means the organization did. The bounce never names the person.
Will changing my sending IP help?
No. The block matches your envelope address or domain, not the IP, so a new server sends into the same block.

All 191 bounce codes