SMTP Error 553 5.1.2 – How to Fix It [SOLVED]

If you’re still asking the question “How do I fix error 553 5.1.2?” you’re in the right place. The following solutions are proven methods to troubleshoot and resolve this error. 

Solution #1: Verify the recipient address for typo errors

Double-check that you have the correct email address and that it is correctly typed in the “To” field. Pay special attention to the domain and look for:

• Common typos (Example: .cmo instead of .com)

• Missing or extra characters
• Spacing errors

Solution 2: Confirm if the domain really exists

Use online tools or DNS lookup services to verify if the recipient’s domain exists and is active. You can use command-line tools like nslookup or dig to check if the domain has valid DNS records.

Solution 3: Check MX records

If you have access to the domain management, verify that the MX records are properly configured. MX records direct email traffic to the correct mail servers. Missing or incorrect MX records will prevent email delivery. 

Solution 4: Contact the recipient through alternative channels

If possible, reach out to the recipient via phone, text, or social media to confirm their correct email address. They may have recently changed domains or might be unaware of issues with their email configuration.

Solution 5: Review your own email client settings

Ensure your email client isn’t adding unwanted characters or formatting email addresses. Sometimes autocorrect features can inadvertently modify addresses.

Solution 6: Clean your email list

If you’re sending to multiple recipients, use email validation services to validate addresses before sending. This helps identify and remove invalid domains from your list.

Similar to SMTP Error 510, manual entries of email addresses can sometimes result in these errors. When sending to only one or a few email addresses, it may only take a few seconds to check for errors. However, it can be very difficult for high-volume senders to run through each and every email address in your list.

That’s why it’s recommended to import the whole list from forms to Warmy’s Validation Tool which checks for any invalid email addresses. 

Warmy users get free 10,000 credits which you can use right away before you launch your next large-scale campaign. Get started today.  

How does SMTP Error 553 5.1.2 affect your email deliverability?

Experiencing 553 5.1.2 Error Code once may not do any significant damage to your email deliverability or sender reputation. However, triggering this error repeatedly can cause long-term damage. 

The consequences of bulk email permanent failure 553 5.1.2 extend beyond individual failed deliveries. Consequences include:

Damaged sender reputation

Email Service Providers (ESPs) and Internet Service Providers (ISPs) monitor bounce rates and delivery failures as closely as possible. Consistently high bounce rates give off the impression that the sender does not practice good email practices. 

When your emails consistently fail to reach recipients due to invalid domains, it raises a red flag and may give the impression that you are trying to send multiple invalid emails, which can translate to spam behavior. Even if you are unaware of this, it can still impact and damage your email health.

Increased spam filtering and potential blacklisting

A decline in sender reputation is more than enough reason for email providers to send you to spam. This can cause ESPs to mark your domain as suspicious and decide to send future emails to the spam folder. Or worse, ESPs may decide to blacklist you. If you get blacklisted, other major providers will again see this as another red flag—further damaging your sender score.

An article from Hubspot confirmed that top-performing campaigns have 2% bounce rates only. So if you have a higher percentage of bounce rates, you will need to act right away.

Lost business opportunities

Beyond technical impacts, failed deliveries also mean missed connections. You might lose potential customers, partnerships, or important communications simply because your emails aren’t reaching their destination.

Prevent SMTP errors with Warmy.io – Here’s how:

Warmy.io provides a full-on email deliverability solution that helps senders build, establish, and maintain long-term email health and sender reputation. Senders with a solid domain health are less prone to experiencing SMTP errors and the damage that comes with them. 

While many alternatives offer basic email warmup to increase email deliverability, Warmy’s full suite of tools work hand in hand to optimize various aspects that affect sender reputation. This includes inbox placement, authentication protocols, sending behaviors, and even email content. 

Warmy uses its proprietary AI, Adeline, to analyze and draw insights from each sender’s data to be able to implement the best deliverability strategy guaranteed to get consistent high inbox placement and less run-ins with SMTP errors. 

Try validating your first few thousand emails for free when you sign up for a Warmy plan. 

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