SMTP Error 450 4.1.1 is a temporary rejection code which typically appears as: 450 4.1.1 recipient@domain.com: Recipient address rejected.
This falls under the “soft bounce” category in email lingo, which means that the server of the recipient cannot accept the email as of the moment, and is suggesting that you can try again later.
Let us explore more about this: why does this occur, and what are the things that you can do to “fix” and avoid it.
Why does SMTP Error 450 4.1.1 occur?
The SMTP Error 450 4.1.1 belongs to the SMTP Error 450, which indicates that the error is a temporary one. Although SMTP errors of this category often means that it can lead to a quick fix, it is still important to understand how this occurs.
This will give you the information you need to potentially avoid and resolve this in the future.
But why exactly does this happen?
- Its sub-code 4.1.1 denotes a “bad destination mailbox address.”
- The “4” pertains to a persistent transient failure, which confirms that the issue is temporary. This means that retrying later can also increase the chance of its sending success.
- Meanwhile, the “1” subject subcode refers to an addressing status problem. It may cover issues like syntax or validity of the originator or destination address.
Receiving this error means that there is a high chance that the local-part before the “@” symbol is invalid or unknown.
But this error can be potentially triggered by varying issues such as:
- Server-side greylisting
- Undergoing maintenance
- Temporary overload delaying acceptance
- Mailbox temporary full
- Misconfigured mailbox
- DNS issues
- Sender reputation
Although very rare, SMTP error 450 4.1.1 can also be due to your email or domain’s questionable reputation. For example, if an email service provider notices that you are sending high volumes of email, there is a slight chance that the service provider might temporarily block you and reject your emails as a precautionary measure while they evaluate your sender behavior.
How to fix SMTP Error 450 4.1.1
There is a long list of SMTP Errors that you should be wary of, and each has its own unique challenges and resolution. Since we’ve established that the SMTP error 450 4.1.1 indicates a temporary email failure, there is a great chance of it being fixed by simply following this guide:
Wait and retry
Since this is a temporary error, your mail server should automatically retry delivery. Most SMTP servers are configured to retry for 24-72 hours before giving up. The issue often resolves itself within minutes or hours.
Check the recipient address and verify mailbox status
Verify that the recipient’s email address is spelled correctly and exists. A simple typo can cause delivery issues. If possible, contact the recipient through an alternative channel to confirm their mailbox is active and has available storage space.
Implement proper email authentication
Check if your domain has proper SPF, DKIM, and DMARC records configured. These protocols are indicators for servers that your domain is trustworthy, which will reduce the probability of temporary rejections.
Monitor your sender reputation
Have your IP address checked and ensure that you monitor your domain reputation. Using tools like Google Postmaster v2, Microsoft SNDS, or Warmy with its Domain Health Hub can help you maintain a strong sender reputation and reduce the chances of temporary rejections.
Use email warmup services
It can be difficult for a new IP address or domain to have an established reputation for email servers. Since they are fairly new, and relatively unknown, email servers do not have a clear gauge if an IP address or domain is authentic and trustworthy. Fortunately, you can use email warm up like Warmy to help you gradually build your sender reputation by slowly increasing your sending volume, and engage with real mailboxes to establish trust with internet and email service providers.
Related Reading: The Science and Process of Warming Up Newly Created Email Domains
Implement rate limiting
Space out your email sends, especially when sending to the same domain. Avoid sudden spikes in sending volume that might trigger rate limiting on the receiving end.
Configure proper retry logic
Ensure your email system has appropriate retry intervals configured. A good practice is to retry after 5 minutes, then 15 minutes, then hourly for the first day, and less frequently afterward.
Maintain clean email lists and email queue
Regularly clean your email lists to remove invalid addresses, inactive recipients, and hard bounces. A clean list improves deliverability and reduces the likelihood of temporary errors.
And ensure that you keep an eye on your email queue for patterns. If you notice multiple 450 errors to the same domain, it might indicate a systemic issue that needs addressing, which means that “waiting it out” may no longer be applicable.
How to prevent severe SMTP errors with Warmy
SMTP Error 450 may be a temporary hurdle, but it can lead to other severe SMTP errors. Having Warmy at your side can give you more control of your email health, and give you complete control and visibility of your mailboxes at a domain level. Here are some of the features you can take advantage of.
Email warmup and reputation building
Warmy’s progressive email warmup system can help you establish your sending domain as a reputable email by gradually increasing your sending volume.
The platform’s dedicated inbox placement test offers real-time visibility into message routing, giving you visibility over whether emails reach the inbox, get filtered to spam, or land in promotional folders. It will also help you understand further if the SMTP error you receive is an issue with your domain or your recipient.
You can also access the free email deliverability test to assess your current sending reputation.
Authentication protocol implementation
The free SPF Record Generator and free DMARC Record Generator provide ways to help you secure configuration over DNS records, and ensure that your domain is trustworthy.
Authentic email interaction through seed lists
Warmy.io’s seed list technology allows organizations to stress-test and optimize campaigns before deploying them to real contacts. Warmy’s seed list employs authentic email accounts that meaningfully interact with your messages. This “interaction” includes:
- It goes beyond simple read receipts by making sure that your messages are opened and reviewed
- Helps demonstrate to email providers that your content generates legitimate interest by naturally clicking on embedded links — if you have one in your email
- Retrieves emails from spam folders, then flags it as important, which is an indicator of a legitimate email for many email and internet service providers.
Complete infrastructure monitoring
Warmy provides a dashboard presenting actionable intelligence on delivery success rates, reputation metrics, and warmup progression over time.
Blacklist monitoring
Continuous monitoring of IP and domain against major blacklist databases. Warmy’s advanced systems alerts you by confirming any potential reputation issues before it becomes a major issue in your deliverability.
Prevent SMTP errors and deliverability issues with Warmy.io
While there are some SMTP Errors that are out of senders’ control, there are still many things senders can do to minimize the likelihood of experiencing these errors.
At the core of it is having a solid sender reputation. Want to secure an ideal email health and reputation? Give Warmy a try for free today!
FAQ
What is SMTP Error 450 4.1.1?
SMTP Error 450 4.1.1 is a temporary rejection code which typically appears as: “450 4.1.1 recipient@domain.com: Recipient address rejected.” It means that the server of the recipient cannot accept the email as of the moment, and is suggesting that you can try again later.
How long should I wait before resending an email that received a 450 4.1.1 error?
You don’t need to manually resend the email. Your mail server will automatically retry delivery multiple times over 24-72 hours. Most temporary issues resolve within 15-30 minutes.
Is SMTP Error 450 4.1.1 a sign that my emails are being marked as spam?
Not necessarily. While this error can sometimes be related to sender reputation concerns, it’s more commonly caused by greylisting (an anti-spam technique), mailbox quota issues, or temporary server problems. However, if you’re seeing this error frequently across multiple domains, it could indicate reputation issues.
Will SMTP Error 450 4.1.1 affect my sender reputation?
Temporary errors like 450 4.1.1 have minimal impact on your sender reputation compared to hard bounces (5xx errors). However, if these errors occur frequently and in large volumes, they can signal underlying problems that may eventually damage your reputation.
