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Undelivered Mail Returned To Sender – Unknown Recipient

If you’ve encountered the “Undelivered Mail Returned to Sender – Unknown Recipient Error,” – you’re not alone.

This can happen for various reasons, but primarily it indicates that the email you sent cannot be delivered to the recipient’s mailbox. In this article, we will explain the error in simple terms and guide you on how to solve it.

What is the “Undelivered Mail Returned to Sender – Unknown Recipient” error?

When you send an email, it passes through several computer systems before it reaches the recipient’s mailbox. During this process, sometimes the email fails to deliver and gets returned to the sender, often with an “Undelivered Mail Returned to Sender – Unknown Recipient” error message.

This error typically occurs when the recipient’s email address is incorrect, does not exist, or the recipient’s mailbox is full or is having issues. If you get this error, it simply means your email couldn’t find a home to land in.

How to fix the “Undelivered Mail Returned to Sender – Unknown Recipient” error?

Fixing this error involves troubleshooting a few things. Here’s what you can do:

Step 1: Check the Recipient’s Email Address

The first thing you need to do is verify the recipient’s email address. It’s easy to mistype an email address, especially if it’s a long one. Check for any spelling mistakes or incorrect domain names (like “” instead of “”).

If you have another way of contacting the recipient, like through a phone call or a text, it may be helpful to confirm the correct email address with them.

Step 2: Check if the Recipient’s Mailbox is Full

Sometimes, the error can occur because the recipient’s mailbox is full. Unfortunately, you can’t fix this problem. The recipient must clear their mailbox to receive new emails. If you can text or call them, let them know their inbox is full and they need to clear it so they can receive email.

Step 3: Consider Using a Different Email Address

If you’ve tried all of the above and are still encountering issues, you might want to consider sending the email to a different email address if the recipient has one.


The “Undelivered Mail Returned to Sender – Unknown Recipient” error can be frustrating, but it’s usually straightforward to fix. The most important thing is to verify the recipient’s email address and to ensure you’ve typed it correctly. That’s usually the number one reason why this error pops up.

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