Outgoing Emails are Bouncing Back

Question

My emails keep bouncing back. I can receive incoming emails but I am unable to send outgoing.

How can I fix this?

Answer 1

Hi Jermaine,

This error comes from Microsoft 365/Exchange Online's protection system and means your account or organization has hit a sending limit. When Microsoft detects too many outgoing emails in a short period or notices activity that looks suspicious, it temporarily blocks sending to prevent spam or abuse.

To resolve the issue, start by checking your Microsoft 365 sending limits, as the service imposes daily and per-minute thresholds such as around 10,000 recipients per day or about 30 messages per minute and exceeding them triggers an automatic block.

If that is the case, you'll need to wait for the restiction to clear; these throttles are temporary and typically lift within 24-48 hours once your activity returns to normal.

Make sure your account hasn't been compromised, since Microsoft will block accounts that appear to be sending spam.

I hope this helps.

Answer 2

Hi,

This is April, I'll be happy to assist you. Sorry to hear that you're having issue with Outlook mail. Let me help you out.

Based on the description of the issue you provided, you can receive incoming emails but are unable to send outgoing messages. Your sent emails bounce back with errors.

Can you share the exact error message or bounce-back code you're seeing when trying to send emails?

If you can receive emails but can't send them, the issue is usually with your SMTP settings, authentication or a network block. Try these steps to fix it:

1. Check your Outbox
   • Look for messages stuck in the Outbox
   • Delete and resend if needed
2. Verify SMTP Server Settings Go to your email account settings and confirm:
   • SMTP server name (e.g., smtp.office365.com for Microsoft 365)
   • Port: Usually 587 (with STARTTLS) or 465 (with SSL)
   • Encryption: TLS or SSL
   • Authentication: Enabled with your full email address and password
3. Confirm Authentication
   • Update your password in Outlook if you recently changed it.
   • Ensure "My outgoing server (SMTP) requires authentication" is turned on.
4. Firewall or Antivirus Interference
   • Temporarily disable your firewall or antivirus to test if they're blocking outgoing mail.
   • If it works, add your email client to the firewall's allowed list.
5. Check Network Restrictions
   • Some ISPs block SMTP ports. Try another network or a mobile hotspot.
   • If it works, contact your ISP or use a VPN
6. Verify Mailbox limits
   • Make sure your mailbox isn't full and that your provider hasn't restricted outgoing mail.
7. Check for Bounce-back error messages
   • Review the exact error message in the bounce-back email. It often includes a code like 550 5.7.1 or messages like "relay denied" or "blocked for spam"
   • These often point directly to the problem.
8. Try Webmail or another Client
   • Login in via webmail (Outlook.com or Gmail.com) and try sending from there.
   • If it works, the issue is with your local email client.

For Outlook or Microsoft 365 users, make sure Outlook isn't set to Work Offline. If the issue continues, creating a new Outlook profile can often resolve persistent sending problems.

I hope this helps. If you need further assistance you can reply to this message.

Thank you,

April P.

Independent Advisor

Answer 3

If your outgoing emails are bouncing back while you can receive incoming emails, it may be due to a configuration issue, such as a Sender Policy Framework (SPF) problem. Here are some steps you can take to troubleshoot and fix the issue:

1. Check the Bounce Message: Look at the non-delivery report (NDR) or bounce message you receive. It often contains diagnostic information that can help identify the issue.
2. Verify SPF Record: Ensure that your SPF DNS record is correctly configured for your domain. You can use a publicly available SPF or DNS record checker to verify this.
3. Provision Domains: Make sure all domains you own are provisioned. Microsoft limits the number of emails sent with unprovisioned domains.
4. Include On-Premises IPs: If you have on-premises servers, ensure their IP addresses are included in your SPF record.
5. Check Spam Filters: Verify that your outbound messages are not being identified as spam by Microsoft 365 or Office 365. If they are, they may be routed through the High Risk Delivery Pool, which can cause SPF checks to fail.
6. Contact Support: If you determine that your messages are incorrectly detected as spam, consider contacting Microsoft support for assistance.

By following these steps, you should be able to resolve the issue with your outgoing emails bouncing back.

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References:

• Fix NDR error "550 5.7.23" in Exchange Online
• Fix NDR error "550 5.1.10" in Exchange Online
• Fix NDR error "550 5.7.13" or "550 5.7.135" in Exchange Online
• Fix NDR error "550 5.1.0" in Exchange Online
• Set up SPF to help prevent spoofing
• High Risk Delivery Pool for outbound messages