Remote Server returned '550 5.7.705 Service unavailable. Access denied,tenant has exceeded threshold

Copper Contributor



I'm not able to send E-Mails for one week now.


If I send an E-Mail I immediately receive a Mail containing the error named in subject.


I need to send mails. Could anybody help?


Thanks in advance!




14 Replies

I already opend a support case and after 3 hours phone with supporter no solution could be found.



You can refer to the article "Tenant has exceeded threshold" NDR when mail is sent from your organization


It describe the causes of it but you can also do the Resolution part.


It says: -> To fix this issue, follow these steps:

  • Remove any unknown or unused inbound connectors from Office 365. To do this, follow these steps:
    Go to Exchange Admin Center, and sign in as an Exchange Online administrator.
    Select mail flow in the left-hand frame, and click connectors.
    If any connectors already exist for your organization, you can see them listed here. If you see any connectors that don't belong, you should remove them by selecting the connector and clicking the Trash icon. The following screenshot shows some sample connectors that you should have if you are in a hybrid scenario. All other connectors should be inspected and removed if they are not required.
    An example of connectors to and from Contoso email server
  • Check the audit logs to determine whether a connector was created recently. Spammers are known to create connectors, send out lots of mail on that connector, and then delete the connector to cover their tracks.
    Because an admin account was compromised, change the passwords for all your admins.
    To prevent future compromise, enable multi-factor authentication (MFA) for, at least, the admin accounts. For more information, see Set up multi-factor authentication.
    Contact Microsoft Support to unblock the tenant.


Thanky for this hint.

All names points (Connectors, Passwords, MFA...) I already checked on my own resprectivly together with and supporter of Microsoft. Unfortunately, nothing worked.


I have not been able to send mails for two weeks now. And nobody at Microsoft seems to be able to identify and fix the reason for the problem.


Then unfortunately I will have to switch to Google :sad:


@Gervs  made a nice point there. That could help.

Hi there I have had problems with this message - Re: Remote Server returned '550 5.7.705 Service unavailable. Access denied,tenant has exceeded threshold and am waiting for a call back.  In the meantime I want to redirect a domain from an existing host to microsoft.  Do Microsoft have to have the the domain to be able to host the email?  I am having to point the name servers to microsoft and Openhost state to do so the domain must be transferred to the new provider.  Is this correct?




Has anyone found a solution to this issue.   I am having the same problem now.

The above blog entry was helpful for me. My office 365 account had been hacked. Deleted a number of new accounts that had created by the attacker. Enabled MFA and reset the admin passwords. Logged a ticket to get the blacklist cleared.
Been waiting for Microsoft since 8th September 2021 and technician does not seem to have the expertise to remove blacklist from tenant. Still cannot send email and client at wits end with support by Microsoft not resolving problem
took support 8 days to resolve - prepare for a long wait if this occurs on your tenant



Hello, did you receive any update for this issues? i have the same issues in the company for 4 users, not able to send emails, seriously thinking about switching to google... \\




Hello, did you receive any solution for this email issues ?