Send & Receive Issues

How to Fix Microsoft 365 Undeliverable Messages (Socket Error 10061)

John Wilson Oct 12, 2026 870 views

Question details

The user is experiencing repeated non-delivery reports (NDRs) in Microsoft 365 indicating that an email has expired or the connection was refused due to Socket Error 10061.

How to Fix Microsoft 365 Undeliverable Messages with Socket Error 10061

Product: Microsoft 365
Device & OS: not provided
Scenario: Sending emails and receiving automated bounce-back messages detailing delivery failure.
Observed behavior: Emails fail to deliver, returning non-delivery reports with error messages such as 'Message Expired', 'connection refused', or 'Socket error 10061'.

Before you start

Verify your internet connection and check if this delivery issue occurs with a single specific email address or multiple different recipients.

Solution 1Recommended

Verify Recipient Details and Secure Your Account

Use this solution to rule out simple typos in the email address and ensure your Microsoft 365 account hasn't been compromised by unauthorized senders.

Socket Error 10061 often occurs when the destination mail server actively refuses the connection. This can be caused by sending mail to a misspelled domain (e.g., hotail.com instead of hotmail.com). Additionally, if you are receiving bounce-backs for emails you didn't send, your account may be compromised.

Check the recipient address

Open the undeliverable message and carefully review the recipient's email address for any typos, especially in the domain name after the @ symbol.

Review your Sent Items and Rules

Navigate to your 'Sent Items' folder and check for outgoing messages you do not recognize. Go to Outlook Settings > Mail > Rules to ensure no hidden forwarding rules have been created by unauthorized users.

Update your password

If you suspect unauthorized activity, immediately change your Microsoft 365 account password through your organization's security portal.

Enable Multi-Factor Authentication (MFA)

Contact your IT administrator or go to your Microsoft account security settings to enable MFA, adding an extra layer of protection against account spoofing.

Verify Recipient Details and Secure Your Account

Spoofing Warning: If someone is 'spoofing' your email address, they are forging your address as the sender. Strengthening your account security will stop emails sent directly from your account, but you may need your IT admin to update SPF/DKIM records to prevent domain spoofing.

Solution 2

Analyze Message Headers and Escalate to IT Admin

When the recipient's address is correct and your account is secure, the destination server itself might be rejecting the connection.

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Frequently Asked Questions

What does Socket Error 10061 mean in Microsoft 365?

Socket Error 10061 translates to 'Connection Refused'. This indicates that your mail server successfully reached the recipient's mail server network, but the recipient's server actively rejected the connection attempt, often due to typos in the domain, server downtime, or strict firewall rules.

Why am I receiving undeliverable messages for emails I never sent?

If you receive non-delivery reports for emails you didn't send, your account might be compromised, or someone is 'spoofing' your email address. You should immediately check your Sent Items, review your mailbox rules for unfamiliar forwarding, change your password, and enable multi-factor authentication (MFA).

Can I fix the connection refused error by myself?

If the error is caused by a simple typo in the recipient's email address, you can fix it by correcting the address and resending the email. However, if the address is correct, the issue usually lies with the destination server or your organization's network routing, which requires intervention from a mail administrator.

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