Summary
The Hotmail 550 5.5.0 mailbox unavailable bounce error is a permanent failure with multiple potential causes. Predominantly, it signifies an issue with the recipient's email address, such as it being invalid, non-existent, or inactive. A full mailbox can also trigger this error. However, it's also important to consider issues with the sender's reputation, including IP blacklisting and spam complaints. Furthermore, Hotmail-specific issues, like database synchronization problems and Microsoft's SmartScreen filter, can contribute to these bounces.
Key findings
- Invalid Recipient Address: The most common cause is an invalid, non-existent, or inactive recipient email address.
- Permanent Failure: The 550 5.5.0 error indicates a permanent failure; resending will likely not succeed.
- Sender Reputation: Blacklisted IPs or domains, as well as spam complaints, can cause this bounce.
- Hotmail-Specific Issues: Hotmail's internal issues, such as database synchronization problems and SmartScreen filtering, may cause the error.
- Mailbox Full: Recipient's mailbox being full can cause this error.
Key considerations
- Verify Recipient Addresses: Always double-check the recipient's email address for any typos or inaccuracies.
- Monitor Sender Reputation: Regularly monitor your sender reputation, including IP and domain blacklists, and address any issues promptly.
- Optimize Email Content: Ensure your email content does not trigger spam filters or Microsoft's SmartScreen filter.
- List Hygiene: Maintain a clean email list by removing inactive or non-existent email addresses.
- Hotmail Quirks: Be aware of Hotmail-specific issues that may cause bounces even when the email address is valid.
What email marketers say
9 marketer opinions
The Hotmail 550 5.5.0 mailbox unavailable bounce error typically indicates a problem with the recipient's email address or mailbox. Common causes include invalid or non-existent email addresses (often due to typos or abandoned accounts), inactive mailboxes, full mailboxes, and potential issues with the sender's IP address or domain reputation. Microsoft's SmartScreen filter and spam complaints can also trigger this error. It is a permanent failure.
Key opinions
- Invalid Address: The most frequent cause is an invalid email address due to typos or the account no longer existing.
- Inactive/Full Mailbox: The recipient's mailbox may be inactive, suspended, or full, preventing message delivery.
- Reputation Issues: Problems with sender reputation (IP blacklisting, spam complaints) can lead to this error.
- SmartScreen Filter: Microsoft's SmartScreen filter may block emails based on content, resulting in the bounce.
Key considerations
- Verify Email Addresses: Always double-check recipient email addresses for accuracy to minimize bounces.
- Monitor Reputation: Actively monitor your IP address and domain reputation to identify and address any issues.
- Content Review: Review your email content to ensure it does not trigger spam filters or Microsoft's SmartScreen.
- Address List Hygiene: Regularly clean your email list to remove inactive or non-existent addresses.
Marketer view
Email marketer from EmailDudes Forum states that the 550 5.5.0 error can mean a number of things, including the recipient's mailbox being full, the account being inactive, or a typo in the email address. They recommend verifying the email address and trying again.
28 Aug 2021 - EmailDudes Forum
Marketer view
Email marketer from Stack Overflow shares that the error means the mailbox is unavailable. Reasons can include that the mailbox doesn't exist (typo in address), the user account is inactive, or the mailbox is full and cannot accept new messages. Also possible the sending IP is blocked.
23 Sep 2022 - Stack Overflow
What the experts say
3 expert opinions
The Hotmail 550 5.5.0 mailbox unavailable bounce error can stem from several underlying issues. One potential cause is Hotmail's internal synchronization problems between MTAs and its backend database. Additionally, the error often signals a refusal to accept the email, commonly due to the recipient address not existing or being inactive. The errors are permanent and should not be retried.
Key opinions
- Database Sync Issues: Hotmail may experience synchronization problems between its mail transfer agents (MTAs) and the backend database of active users, leading to this error.
- Non-Existent Address: The recipient's email address may not exist on the mail server.
- Inactive Mailbox: The recipient's mailbox might be inactive.
- Permanent Failure: 550 errors mean the message cannot be delivered to that recipient.
Key considerations
- Address Validation: Always validate email addresses to ensure they exist and are active, but be aware there can be MTA issues outside of your control.
- Internal Errors: Be aware that Hotmail may produce this error even if the address is valid due to its own internal problems.
Expert view
Expert from Word to the Wise notes that 550 errors are permanent failures, meaning the message cannot be delivered to that recipient. 5.5.0 often means the recipient mailbox doesn’t exist on the mail server or the recipient’s mailbox is inactive.
2 Dec 2023 - Word to the Wise
Expert view
Expert from Email Geeks explains that mailbox unavailable is usually not spam related. Hotmail often loses sync between the MTAs and backend database, causing this bounce error.
28 Feb 2022 - Email Geeks
What the documentation says
5 technical articles
Documentation consistently indicates that the Hotmail 550 5.5.0 mailbox unavailable bounce error is a permanent failure primarily caused by an invalid recipient email address. It can also stem from the mailbox being unavailable due to policy reasons or general issues with the recipient's server. It is best not to reattempt sending when you receive this error.
Key findings
- Permanent Failure: The 550 5.5.0 error is a permanent failure, signifying that the message cannot be delivered.
- Invalid Address: A common cause is an invalid or non-existent recipient email address.
- Mailbox Unavailable: The mailbox might be unavailable due to policy reasons or server-related issues.
Key considerations
- Verify Addresses: Always verify the recipient's email address for accuracy.
- Avoid Resending: Given the permanent failure status, avoid resending the message.
- Check Error Details: Consult specific error messages from the mail server for detailed information.
Technical article
Documentation from Microsoft Support explains that the 550 5.5.0 error is a general permanent failure. It usually means the recipient's email address doesn't exist. Double-check the recipient's email address for typos and ensure it's correct.
11 Dec 2023 - Microsoft Support
Technical article
Documentation from RFC Editor explains that 5.X.X status codes indicates a permanent failure. The message should not be sent again. Specifically, the 5.5.0 code indicates that the address is invalid for the mailbox.
12 Jan 2023 - RFC Editor
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