mails from mx.easyname.com are not delivered

Question

this ist

this is the second time i do not get mails sent from a easyname.com domain, maybe you can whitelist 77.244.243.83 or all other mx.easyname.com IPs ?

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This message was created automatically by mail delivery software.

A message that you sent has not yet been delivered to one or more of its

recipients after more than 4 hours on the queue on mx.easyname.com.

 

The message identifier is:     1vvm2d-000GAy-8Z

The subject of the message is:

=?UTF-8?Q?WG:_Office_Lizenzen_f=C3=BCr_Infinity?=

The date of the message is:    Fri, 27 Feb 2026 01:49:12 +0100

 

The address to which the message has not yet been delivered is:

 

  ******@freunberger-it.at

    host freunbergerit-at02i.mail.protection.outlook.com [52.101.68.29]

    Delay reason: SMTP error from remote mail server after pipelined sending

data block:

    451 4.7.500 Server busy. Please try again later from [77.244.243.83].

(S77719) [DU2PEPF00028D10.eurprd03.prod.outlook.com 2026-02-27T04:51:03.278Z

08DE7595D7AA887B]

 

No action is required on your part. Delivery attempts will continue for

some time, and this warning may be repeated at intervals if the message

remains undelivered. Eventually the mail delivery software will give up,

and when that happens, the message will be returned to you.

Answer 1

The NDR shows this error from Exchange Online Protection (EOP):

451 4.7.500 Server busy. Please try again later from [77.244.243.83]. (S77719)

This means Microsoft 365 has temporarily throttled or restricted mail from the sending IP 77.244.243.83 because of suspicious or high-volume activity. It is a transient (4.x) error, so the sender’s server will keep retrying; if the traffic is later judged acceptable, delivery will start succeeding again.

For the sender (mx.easyname.com / 77.244.243.83):

1. Review outbound mail for spam or compromised accounts that might have caused the throttling.
2. Follow Microsoft’s guidance for external senders to Microsoft 365 to ensure the sending environment is compliant (SPF, DKIM, DMARC, proper volume, no spam content). See the external-sender troubleshooting article referenced below.
3. If NDRs change to a 5.7.6xx “Access denied, banned sending IP” style error (for example 550 5.7.606–649), use the Office 365 Anti-Spam IP Delist Portal at https://sender.office.com to request removal from the blocked senders list, as documented.
4. If the error remains 4.7.500 for an extended period, the sender should still review their reputation and sending patterns; throttling is automatic and based on risk signals.

For the Microsoft 365 recipient tenant (freunberger-it.at):

1. Because this is a service-side throttling decision, there is no direct “whitelist this external IP” option documented for this specific 4.7.500 condition.
2. Verify that the recipient address is valid and working for other senders.
3. If the issue persists and affects legitimate business mail, open a support case with Microsoft 365 support, providing:
   • The full NDR text
   • Sending IP (77.244.243.83)
   • Message ID and timestamps Microsoft support can review the throttling decision and advise further.

The message text from mx.easyname.com already indicates that no action is required by the sender for now and that delivery attempts will continue. If the throttling is temporary and the sender’s reputation is acceptable, the messages should eventually be delivered.

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References:

• External senders - Troubleshoot email sent to Microsoft 365
• External senders - Use the delist portal to remove yourself from the blocked senders list and address 5.7.511 Access denied errors
• Email non-delivery reports and SMTP errors in Exchange Online