MICROSOFT 365 / OUTBOUND MAIL
This error means Exchange Online refused outbound traffic from a sending IP with low reputation. Microsoft says new customers, including trial subscribers, are more likely to encounter it.
Checked against Microsoft Learn on October 7, 2026. The code does not, by itself, prove account compromise, a DNS fault or a particular fix.
Accepted is not delivered.
Most transport work happens after Graph returns HTTP 202.
START WITH THE EVIDENCE
Microsoft Graph returns HTTP 202 after it creates and saves the message for processing. Exchange then moves the message into transport, and a copy can appear in Sent Items before later policy checks, routing and delivery finish. Review the nondelivery report and Message Trace. A sent copy alone does not prove the recipient received the message.
Record the error code, sender, recipient and time privately. Use that evidence to inspect the one failed path instead of repeatedly sending more messages from the same tenant.
SAFE ADMINISTRATOR CHECKS
Confirm the intended mailbox has the required Exchange Online service and review subscription and service health. Microsoft directs trial customers who receive 5.7.708 to Support to request an IP exception until Exchange Online licenses are assigned.
Confirm the sending domain is added and validated in Microsoft 365. Compare MX and authentication records with the intended setup before changing them. An unregistered sending domain is associated with a different error, 5.7.750.
Review intended mail-flow connectors and investigate anything unexpected. Microsoft names compromised administrators and unusual connectors as causes for related outbound restrictions. Do not weaken security or create an open relay to work around a block.
Check Microsoft Defender for blocked users. A clear user list does not prove that no tenant- or service-level restriction exists; these are different controls.
Review suspicious sign-ins, unknown forwarding or inbox rules, unexpected administrative changes and unusual Sent Items. Follow Microsoft's compromised-account procedure when the evidence supports it.
Use Message Trace to determine whether the service received, rejected, deferred or delivered the message and which actions occurred before the final status. Keep recipients, message identifiers and exports private.
Protect administrator and sending identities with MFA, review alerts and Secure Score recommendations, and remediate confirmed problems before requesting restoration.
Exchange Online is not a bulk-mail platform. Microsoft recommends a purpose-built bulk service when volume requires one. Keep routine customer correspondence distinct from campaigns and automated application traffic.
WHO CAN REMOVE THE BLOCK
For trial-related 5.7.708, Microsoft's published instruction is to contact Support for an IP exception until Exchange Online licenses are assigned. For related tenant-level outbound blocks, Microsoft instructs administrators to address the underlying cause and then contact Support to remove the block.
A DNS correction, security review or technology assessment cannot guarantee unblocking, delivery restoration or a restoration time. Microsoft controls its service and restriction decisions.
YOUR NEXT STEP
Run the free Email and DNS Security Check to inspect public MX, SPF, DKIM hints, DMARC, MTA-STS, TLS-RPT, DNSSEC and CAA records in your browser. It cannot inspect licenses, sign-ins, connectors, Message Trace or Microsoft's internal restriction state.
One remote site or workflow, up to 90 minutes, written priorities and a proposed next step. Choose Mail systems / migration. Timing is agreed when scheduling; configuration, implementation and ongoing support are separate. The assessment does not promise a diagnosis, delivery restoration or Microsoft unblocking. Read the scope and booking terms.
Do not submit passwords, tokens, customer messages, tenant identifiers or unredacted logs. Inquiries are reviewed for U.S. businesses, with Atlanta, Dallas–Fort Worth and Houston as the launch focus.
PRIMARY SOURCES
This guide is general technical information. Microsoft may update service behavior and documentation; use the current NDR, Message Trace and Microsoft Support case for the affected tenant.