Blocked Senders policies define criteria for automatically blocking an email. By default, you will automatically have a policy scoped for the default Blocked Senders Profile Group. If you simply need to block another address or domain for your whole account, you should add it to that Profile Group.

Example of use cases for this policy include preventing users from receiving external emails or preventing users from emailing to certain domains.

When an email is blocked by Mimecast, its content is not kept, so cannot be released or recovered by Mimecast.



  1. Log into your Mimecast Account at
  2. Select Administration Console

  1. Go to ‘Administration > Gateway > Policies’

  1. Click into Blocked Senders

  1. Select New Policy

  1. Give the policy a name (Policy Narrative)
  2. Set Blocked Sender Policy to Block Sender

  1. Set the scope for the policy under Emails From and Emails To

  1. If you want to scope the policy to block emails only when connecting from certain IP Ranges, enter the IPs under Source IP Ranges

Note: You must enter the IP Ranges in CIDR format (For single IPs add /32 at the end)

  1. Press Save & Exit

A Blocked Sender policy will always apply before a Permitted Sender policy, so a whitelisted sender may still get blocked by these policies.