Can't send emails

Question

Can't send emails

Bob Mather 0

Can't send emails get an error message

550 5.1.8

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2 answers

Your answer

Answer 1

The error 550 5.1.8 "Access denied, bad outbound sender" usually means the sending account is blocked or not authorized to send emails.

This can happen in both business (Microsoft 365) and personal accounts, so here are the complete possibilities and fixes:

🔹 If this is a WORK / ORGANIZATION account

This error most commonly means your account has been temporarily blocked from sending emails.

Reasons:

Sending limit exceeded (too many emails)
Suspicious activity detected
Account flagged as spam sender

✅ Fix:

You need to contact your IT administrator and ask them to:

Go to Microsoft Defender portal
Check Restricted entities
Find your email account
Click Unblock

⏱️ Note: It may take up to 1 hour after unblocking to work again.

Also ask admin to:

Check if your account is compromised
Reset password if needed

🔹 If this is a PERSONAL account (Outlook/Hotmail)

Then possible causes are:

Temporary Sending Block

Microsoft may block sending due to unusual activity

👉 Fix:

Wait a few hours and try again
Try sending fewer emails

Incorrect "From" Address

If you're sending from an alias or different email:

👉 Make sure:

The email address exists
It is verified in your account

SMTP / App Configuration Issue

If using mobile app or email client:

Check:

Correct SMTP settings
Proper authentication enabled

Account Security Issue

Try:

Sign in to your account
Complete any security verification prompts

🔹 Quick Test

Try sending email from Outlook Web (browser)
If it fails there too → account-level issue
If it works → app/config issue

✅ Summary

This error usually means:

Your account is blocked from sending, or
You're using an unauthorized sender address

✔️ For work accounts → Admin must unblock

✔️ For personal accounts → wait, verify account, or fix sender settings

If the issue continues, share:

Account type (work/personal)
Where you're sending from (web/app)

So more precise troubleshooting can be done.

Answer 2

Since you didn't specify your account type, I will provide solution based on the tag of your initial post. If you're using a personal account (@hotmail, @gmail, @outlook.com...) please let me know so that I can provide guidance with more accuracy.

Hi Bob,

The message “550 5.1.8 Access denied, bad outbound sender AS(42004)” typically appears in Microsoft Exchange Online or Office 365 environments when an email is blocked because the sender address is not authorized to send mail through that tenant. This issue is often related to the account exceeding sending limits in Exchange Online.

In this case, if you're an end user in your organization, you have to notify your IT administrator.

Please request your administrator to remove a user from the Restricted entities page in Microsoft Defender.

Go directly to this link Security & Compliance
On the Restricted entities page, you’ll see a list of blocked users, domains, and apps.
Use the search bar to find the user by their email address.
Select the user account you want to unblock.
Click Unblock at the top of the page.

Please note that restrictions are usually removed within 1 hour.

Additionally, ask your administrator to check your account for signs of compromise and apply security measures to prevent future issues.

You can refer more via:

However, if this response does not align with the exact error message you're receiving or the issue you're experiencing, please feel free to share additional details. I'd be happy to take a closer look and assist you further.

Thank you for your patience and understanding.

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