Since July 2019, Email DLP has implemented the following sending limits per tenant or per user.
These limits apply uniformly regardless of the service in use (Google Workspace / Microsoft 365) or the delivery destination (internal/external delivery).
When a sending limit is triggered, Email DLP returns an error to Google Workspace / Microsoft 365.
We appreciate your understanding as we strive to maintain stable service.
If you have any questions, please contact HENNGE One Technical Support.
January 13, 2021: Improved error messages to make it easier for users to identify the cause.
May 12, 2021: For some blacklist restrictions, admins can now remove the restriction.
October 24, 2022: Added restriction 1.3 to section 1. Sending Limits.
December 24, 2025: Added section 3. Emails suspected as spam.
If you do not require Email DLP filtering for bounced users (email addresses) used for purposes such as automatic sending, you can send emails without passing through Email DLP by following the steps in the article below.
How to bypass HENNGE Email DLP for specific senders (Microsoft 365)
1. Sending Limits
1.1
[ Error Code ] 450 (Temporary Error)
[ Error Message ] Peak SMTP relay limit exceeded.
[ Details ] This restriction is applied when the number of recipients sent from a specific sender address exceeds 600 recipients within 10 minutes.
The restriction will be removed once normal traffic resumes.
Emails that triggered the sending limit will be automatically resent. (*1)(*2)
1.2
[ Error Code ] 550 (Permanent Error)
[ Error Message ] Daily SMTP relay limit exceeded.
[ Details ] This restriction is applied when the number of recipients sent from a specific sender address exceeds 10,000 recipients per day (24 hours).
The restriction will be removed once normal traffic resumes.
Emails sent during the restriction will not be resent.
The sender must resend the email to the recipients listed in the NDR. (*1)(*2)
1.3
[ Error Code ] 450 (Temporary Error)
[ Error Message ] Peak concurrent SMTP relay limit per sender exceeded.
[ Details ] This restriction is applied when the maximum number of concurrent SMTP connections allocated per sender is exceeded for a specific sender address.
The restriction will be removed once normal traffic resumes.
Emails sent during the restriction will be automatically resent. (*1)(*2)
2. Blacklist
2.1
[ Error Code ] 550 (Permanent Error)
[ Error Message ] We detected a high volume of bounced emails coming from [you/your organization] over a short period of time. To protect our users from spam, emails from [you/your organization] have been blocked. [You/Your organization] will be automatically unblocked in <remaining block duration>. For further assistance, please contact the system administrator.
[ Details ] This restriction is applied when a large number of bounced emails are detected in a short period.
The sending restriction will be automatically removed after the duration specified in the error message.
Additionally, admins can manually remove the restriction from the Email DLP Administration (How to remove).
Emails sent during the restriction will not be resent.
The sender must resend the email to the recipients listed in the NDR.
2.2
[ Error Code ] 550 (Permanent Error)
[ Error Message ] We detected a persistently high volume of bounced emails coming from [you/your organization].To protect our users from spam, emails from [you/your organization] have been blocked.
[You/Your organization] will be automatically unblocked in <remaining block duration>.For further assistance, please contact the system administrator.
[ Details ] This restriction is applied when a persistently high volume of bounced emails is detected.
The sending restriction will be automatically removed after the duration specified in the error message.
Additionally, admins can manually remove the restriction from the Email DLP Administration (How to remove).
Emails sent during the restriction will not be resent.
The sender must resend the email to the recipients listed in the NDR.
2.3
[ Error Code ] 550 (Permanent Error)
[ Error Message ] We detected an unusual rate of unsolicited emails coming from [you/your organization]. To protect our users from spam, emails from [you/your organization] have been blocked. [You/Your organization] will not be automatically unblocked. For further assistance, please contact the system administrator.
[ Details ] This restriction is applied when an unusual number of suspicious emails is detected.
This sending restriction will not be automatically removed.
To remove the sending restriction, stop the relevant email sending by the user and have the admin contact HENNGE One Technical Support.
Once the sender has reviewed the recipients (*), we will remove the sending restriction.
*We can also provide a bounce list to help you review (clean up) the recipients that caused the bounces.
Emails sent during the restriction will not be resent.
The sender must resend the email to the recipients listed in the NDR.
2.4
[ Error Code ] 550 (Permanent Error)
[ Error Message ] Action has repeatedly been taken against [you/your organization] for sending unsolicited emails, but the issue was not solved. To protect our users from spam, emails from [you/your organization] have been blocked. [You/Your organization] will not be automatically unblocked. For further assistance, please contact the system administrator.
[ Details ] This restriction is applied when multiple sending restrictions are detected within a certain period.
This sending restriction will not be automatically removed. If the restriction is triggered multiple times, removal will be performed 24 hours after the restriction was applied.
To remove the sending restriction, stop the relevant email sending by the user and have the admin contact HENNGE One Technical Support.
Once the sender has reviewed the recipients (*), we will remove the sending restriction.
*We can also provide a bounce list to help you review (clean up) the recipients that caused the bounces.
Emails sent during the restriction will not be resent.
The sender must resend the email to the recipients listed in the NDR.
3. Emails Suspected as Spam
Even if an email delivery does not meet the conditions described in "1. Sending Limits" or "2. Blacklist" above, the system may apply a sending restriction to the target address if it determines, based on its own criteria, that the delivery is spam. (*3)
If this restriction is applied, HENNGE One Technical Support will contact the admin to discuss the situation and the steps for lifting the restriction.
(*1) Email DLP analyzes emails per recipient, so the restriction is applied per recipient.
For example, if a single email is addressed to three recipients, it counts as three recipients.
(*2) Email service providers, including Google Workspace, Microsoft 365, mobile carriers, free email services, and anti-spam organizations (such as RBL information providers), may register the sender's IP address on a blacklist if a large volume of emails is sent from a specific sender. This safety feature is implemented to prevent potential impact on email delivery for other users and tenants.
(*3) Sub-address format email addresses are also treated as the same sender.
For example, if myname@example.com is subject to a restriction, sub-addresses such as myname+work@example.com or myname+news@example.com will also be treated as the same address and subject to the restriction.
Generally, "sub-address" is also called "plus addressing," a feature that allows delivery to the original email address even if you add a "+" and any string to the local part (before the @) of the email address.
For more details about sub-addresses, please refer to the following article.
What is a sub-address?