Mailbox blocked daily

Hi AtanasM,

To avoid the blocking of the mailbox you can try to whitelist the mailbox:

o whitelist the mailbox and ensure that messages from its email address are trusted by the security system, you can take the following specific steps in Microsoft Exchange:

1. Access Exchange Admin Center (EAC):

   • Sign in to your Microsoft Exchange Admin Center (https://admin.exchange.microsoft.com) using your admin credentials.

2. Navigate to "Mail Flow":

   • In the EAC, go to "Mail Flow" from the left-hand navigation menu.

3. Select "Rules":

   • Click on the "Rules" tab under "Mail Flow."

4. Create a New Rule:

   • Click on the "+" icon or "Add" button to create a new rule.

5. Name the Rule:

   • Give the rule a descriptive name, such as "Whitelist Mailbox"
     
     

      

6. Configure the Rule Conditions:

   • In the "Apply this rule if..." section, set the conditions to match messages from the specific email address of the mailbox you want to whitelist.
   • For example, choose "The sender is..." and enter the email address of the mailbox in question.

7. Set the Action:

   • In the "Do the following..." section, choose the action to be taken when the conditions are met.
   • Select "Modify the message properties" and then "Set the spam confidence level (SCL) to..." Set it to the lowest value, which indicates the message is not spam (e.g., -1).
     
     

      

8. Save the Rule:

   • Click "Save" to save the new rule.

Can you find the exact reason the mailbox is being blocked in Defender? It may be because it's exceeding some limits (check your outbound anti-spam policy). Generally Microsoft limit outgoing mail to protect both the service and their sending reputation. They recommend using third party services for bulk mail if it exceeds the limits.