Since July 2019, Email DLP has implemented the following sending limits on a per-tenant or per-user basis.
These limits apply uniformly regardless of the service you use (Google Workspace / Microsoft 365) or the delivery destination (internal/external delivery).
When a sending limit is triggered, Email DLP will return an error to Google Workspace / Microsoft 365.
We appreciate your understanding as we work 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. Traffic Limits.
December 24, 2025: Added section 3. Emails suspected as spam.
1. Traffic Limits
1.1
[ Error Code ] 450 (Temporary Error)
[ Error Message ] Peak SMTP relay limit exceeded.
[ Info ] 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.
[ Info ] This restriction is applied when the number of recipients sent from a specific sender address exceeds 10,000 recipients in one 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 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.
[ Info ] This restriction is applied when a specific sender address exceeds the maximum number of concurrent SMTP connections allocated per sender.
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.
[ Info ] This restriction is applied when a large number of bounced emails are detected in a short period.
The 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 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.
[ Info ] This restriction is applied when a large number of bounced emails are continuously detected.
The 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 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.
[ Info ] This restriction is applied when an abnormal number of suspicious emails are detected.
This restriction will not be automatically removed.
To remove the restriction, users must stop sending the relevant emails and admins should contact HENNGE One Technical Support (Important notes on removal).
Emails sent during the restriction will not be resent.
The sender must resend 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.
[ Info ] This restriction is applied when multiple sending restrictions are detected within a certain period.
This restriction will not be automatically removed.
To remove the restriction, users must stop sending the relevant emails and admins should contact HENNGE One Technical Support (Important notes on removal).
Emails sent during the restriction will not be resent.
The sender must resend 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. Traffic Limits" or "2. Blacklist" above, the system may impose sending restrictions on the target address if it determines, based on its own criteria, that the delivery is spam. (*3)
When this restriction is applied, HENNGE One Technical Support will contact the admin to discuss the situation and the steps for lifting the restriction.
(*1) Because Email DLP analyzes emails per recipient, 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 providers, 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-addressing" is also called "plus addressing," a feature where adding a "+" and any string to the local part of the email address (before the "@") will still deliver to the original email address.
For more details about sub-addresses, please refer to the following article.
[Email DLP]What is a subaddress?