Table of contents

Email blocking policy

This document outlines the policy for blocking emails, and deleting emails through administrative processes across email services across the Ministry of Justice (MoJ) estate. It specifically highlights the reasons for active inclusion on an email blocklist and removal from MoJ mailboxes.

To help identify formal policy statements, each is prefixed with an identifier of the form:, where xxx is a unique ID number.

Related information

Acceptable use of Information Technology at work

Data Security and Privacy

Email blocking process

Malware Protection Guide - Overview

Data Handling and Information Sharing Guide

Email Security Guide


This policy applies to all email domains and gateways managed by the MoJ, across all the applicable email services. Specifically, this policy applies to both email traffic inbound (before it reaches the MoJ), and outbound (before it leaves the MoJ).

Blocklist definition

A blocklist is a real-time list, consisting of elements such as IP addresses, network ranges, domain names, email addresses, URLs, and other email characteristics. The common characteristic of the elements is that the sender is suspected of delivering spam.

The blocklist primary purpose is to prevent emails from entering or leaving the MoJ email services. Blocking emails is part of the overall cyber security strategy, providing defence-in-depth on MoJ managed email platforms.

Email types considered for blocking or removal include:

  • Malicious emails.

  • Phishing emails, including derivatives such as vishing, spearfishing, and whaling attacks.

  • Spoofed or impersonation emails.

  • Emails that cause disruption to the availability of an MoJ email service.

  • Other harmful or threatening emails.

Blocking policy

POL.EBL.001: All email services used by the MoJ shall have the ability to add items to the blocklist. The MoJ Security team shall have the appropriate permissions to update and review each MoJ email service blocklist.

POL.EBL.002: Any item added to an email service blocklist should be replicated across the different services in use across the MoJ estate.

POL.EBL.003: Blocklist items added are regularly reviewed to ensure the relevance of the block. Timeframes for reviews reflect the retention policies on the individual email services. Any changes that are made as a result of a review shall be completed and documented under change or incident management processes.

POL.EBL.004: When establishing the criteria for adding an item to the blocklist, the MoJ should go through an impact assessment to establish the impact of adding the specific item to the internal blocklist. If the impact might be substantial, for example causing widespread disruption, or where legitimate emails might be blocked, then the blocking object should be reconsidered or rescoped.

POL.EBL.005: As part the review process, or as a result of a user reported issue such as an incident reported through a user’s local IT Team, a legitimate email might become blocked because it is now on a blocklist. This might be where the email address was added to the blocklist manually, or incorrectly flagged by automated tools in the email system. In this scenario, the MoJ should promptly unblock affected emails, and re-evaluate the blocking rule responsible, in line with this policy. This unblock should happen through the incident management process. All users are encouraged to speak with their Local IT team about concerns with email delivery, or email blocking.

POL.EBL.006: In the event that a legitimate email is blocked by an automatic vendor driven process, or included as an “indicator of compromise” through a threat intelligence product, the MoJ might request that the object be reviewed or reclassified.

POL.EBL.007: Before adding any object to the blocklist, or automatically removing it from an MoJ mailbox, impact analysis shall be carried out and documented through the MoJ change/incident management process.

Deletion of existing emails in scope for blocking

POL.EBL.008: As part of the blocking procedure, the Security team should have the ability to delete or purge emails across the estate which match the blocking criteria listed in the blocklist. This is an optional step, done at the discretion of the Security team.

POL.EBL.009: Purging of existing emails which have been added to the blocklist shall be done under peer review. Peer review should be completed by an independent member of the team who is not involved directly in the analysis or investigation of the email. Peer review takes place only if there is a further threat of users interacting with the newly classified email.

POL.EBL.010: If deletion of emails takes place, then details of the criteria should be included as part of the documentation process recorded as part of change or incident management.

POL.EBL.011: Where appropriate, users are encouraged to delete for themselves any emails confirmed to be in scope for blocking or deletion. Deletion of emails by the Security team should take place only where there is a significant number of users who received the newly classified email.

POL.EBL.012: Removing emails from recipient mailboxes is a viable alternative to adding emails to an email blocklist. This should be the preferred option to prevent users from interacting with emails considered for blocking or removal.

POL.EBL.013: Deletion of emails should be done in such a way that the email could be recovered if required. If this is not possible, the email should be moved to the users ‘junk’ folder rather than simply being deleted.

POL.EBL.014: Users should be made aware of the deletion of emails. However, this is not mandatory.

POL.EBL.015: The MoJ has no responsibility to delete emails from unmanaged MoJ mailboxes.

POL.EBL.016: Automatic deletion of emails for users should be done through automated processes. The Security team shall minimise access to the mailbox from which unwanted emails are purged.

Automated blocking tools

POL.EBL.017: MoJ email services should come with inbuilt vendor managed blocking facilities based on known Indicators of Compromise (IOC’s) to prevent emails entering or leaving the MoJ email environments. This vendor managed list can either be done through general lists of IOCs, or heuristic scanning.

POL.EBL.018: The email service vendor should provide the MoJ with the ability to reclassify incorrectly classified emails. This reclassification process should be accessible to the MoJ Cyber Security team, as well as email administrators.

The Cyber Security Team encourages the integration with 3rd party threat intelligence feeds from trusted providers as part of the in-depth defence strategy.

Blocking or deleting received emails

POL.EBL.019: Any MoJ user who receives an email suspected to be one of the types described previously can request that the email be blocked, preventing future similar emails from being received. On receipt of this, the MoJ reviews the evidence and determines if addition to a blocklist is appropriate. Further actions taken follow the policy statements in this guidance.

POL.EBL.020: Addition of emails to the blocklist is completed by either the local email service management team, or by the Security team. If the former, then approval shall be obtained from the Security team.

POL.EBL.021: In the event that an email is causing widespread disruptions or impacting business, then the individual email administration team responsible for the email platforms can delete emails or place blocks on emails without prior approval. This should be done under change and incident management, with notifications sent to the Security team.

POL.EBL.022: The MoJ shall provide a way for users to request emails for review by the relevant teams.

Preemptive blocking

POL.EBL.023: If MoJ security receives intelligence about a credible threat to the confidentiality, integrity, or availability of an MoJ managed email service, then those emails should be added to the blocklist. Before blocking according to this policy statement, the intelligence should go through an impact analysis.

POL.EBL.024: All blocks should remain in place until the threat is no longer a credible threat to the MoJ.

POL.EBL.025: Email from previously known or blocked items may be re-added to the list if there is credible information or grounds to do so.

Automatic blocking of emails based on attachments

POL.EBL.026: The MoJ should be able to restrict the delivery or sending of emails with certain malicious file attachment types.

POL.EBL.027: A complete list of email attachments blocked should be kept and managed by the individual email administrators, and should be consistent across different email services in use across the MoJ estate.

Contact details

For any further questions or advice relating to security, contact:


If you have any questions or comments about this guidance, such as suggestions for improvements, please contact: