Blocking Attachment Sending for O365 User Mailbox

Blocking Attachment Sending for O365 User Mailboxes, Apply only to specific file types

To block users from sending attachments in Office 365, you can use Exchange Online (part of Microsoft 365) to create a mail flow rule. Here's how you can block attachments for a user mailbox:

Steps:

1. Log in to the Microsoft 365 Admin Center:

   • Go to https://admin.microsoft.com and log in with an admin account.

2. Access the Exchange Admin Center:

   • In the left navigation pane, select Admin centers and then choose Exchange.

3. Create a Mail Flow Rule:

   • In the Exchange Admin Center, go to mail flow on the left side.
   • Click + (Add a new rule) and choose Create a new rule.

4. Configure the Rule:

   • Name the rule (e.g., "Block attachments for specific user").
   • Under Apply this rule if…, select The recipient is... and choose the user you want to block attachments for.
   • Under Do the following..., select Reject the message with the explanation and enter a rejection message (e.g., "Attachments are not allowed to be sent").

5. Add Condition to Block Attachments:

   • Under Add a condition, select Attachment type and choose has attachment to ensure the rule is applied only to emails with attachments.

6. Save and Test the Rule:

   • After configuring, save the rule.
   • Test it by sending an email with an attachment from the blocked user to ensure the rule works.

This will block attachments from being sent from that specific user's mailbox.

Note : This will block mail total size larger than the specified size by design if you specified the size.