we have an email outgoing issue that we can not send to other domains.

Question

Dears, we are facing an issue of sending emails to other domains and we have been advised to purchase upgraded one .

Answer 1

Dear @Saif Hamad

I understand your confusion. However, to help determine the cause, could you please provide the exact error message or non-delivery report (NDR) received when sending emails to recipients outside your organization? This information will help identify whether the issue is related to mail flow configuration, outbound spam protection, domain settings, licensing, or another service-related restriction. For reference: Email nondelivery reports and SMTP errors in Exchange Online

• Are all users affected or only specific mailboxes?
• Does the issue occur when sending to all external domains or only certain domains?
• Are inbound emails from external domains being received successfully?
• Have there been any recent changes to mail flow rules, connectors, or security policies?
• Which Microsoft 365 or Exchange subscription are you using?

In the meantime, if Microsoft 365 users cannot send to any external domain, here are some things you can check:

Step 1: Check if Microsoft has restricted outbound sending.

Microsoft 365 Defender > Email & collaboration > Review > Restricted entities. If the tenant or mailbox has been restricted due to suspected spam activity, outbound mail will be blocked. For reference: Remove blocked users from the Restricted entities page

Step 2: Review Message Trace

Go to: Exchange Admin Center > Mail flow > Message trace > Search for a failed outbound message and review: Status, Event details, and Error code. Whether the message was dropped, deferred, or blocked. For more information, please follow: Message trace in the Exchange admin center in Exchange Online

If you have any questions or if I have misunderstood anything, please feel free to reach out. I'm looking forward to your update.

Answer 2

If outbound mail to other domains is failing, the supported causes in this scenario are usually domain configuration or connector issues, not a requirement to buy an upgraded plan.

Check these items first:

1. Verify the sending domain is added and validated in Microsoft 365.
   • In Microsoft 365 Admin Center, go to Settings > Domains.
   • Confirm the domain used by the mailbox is set up correctly.
   • If the domain is not healthy or not fully configured, external sending can fail.
2. Verify the domain is an accepted domain in Exchange Online.
   • In Exchange Admin Center, go to Mail flow > Accepted domains.
   • Microsoft 365 can block sending from an unregistered or unaccepted domain.
3. If the NDR includes 550 5.7.750 Client blocked from sending from unregistered domain:
   • Add and validate all domains used to send mail.
   • Review outbound connectors. A misconfigured connector can also cause this.
   • Check for unusual connectors or compromised accounts.
   • After fixing the cause, Microsoft Support must remove the block.
4. If the domain uses full redelegation and the error mentions SPF failure:
   • Use nslookup to confirm the NS records point to Microsoft 365:
     • ns1.bdm.microsoftonline.com
     • ns2.bdm.microsoftonline.com
     • ns3.bdm.microsoftonline.com
     • ns4.bdm.microsoftonline.com
   • Check the TXT/SPF record. It should resemble:
     • v=spf1 include:outlook.com ~all
   • If redelegation was set up recently, wait up to 72 hours.
5. If connectors are being used for outbound mail:
   • Review connector configuration carefully.
   • If using a certificate-based outbound connector, the certificate domain must be an accepted and validated domain in Microsoft 365 or Office 365.

The most direct next step is to collect the exact NDR or bounce code from a failed message and match it to the domain or connector issue above.

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References:

• NDR error codes 550 5.7.703, 550 5.7.705, 550 5.7.708, and 550 5.7.750
• You can't send email messages in Microsoft 365 from a domain that's set up for full redelegation
• Can not send email - Microsoft Q&A