Did you know that a hard bounce rate higher than 3% can severely damage your sender reputation? Bounces are not simple bounces – they represent critical signals about the effectiveness of your email marketing campaigns.

The process is simple: when you send an email, two types of bounces can occur. Soft bounces signal temporary problems, such as a full mailbox. Hard bounces, on the other hand, indicate permanent problems that demand your immediate attention.

The key to success in email marketing lies in maintaining a bounce rate below 2%. However, many professionals find it difficult to manage these bounces correctly.

We will show you step by step the differences between soft bounce and hard bounce. You will learn their main causes and, more importantly, effective strategies to prevent them. The goal: to protect your sender reputation and improve the deliverability of your campaigns.

What are soft bounce and hard bounce in email marketing?

When you send an email and it doesn’t reach its destination, what we call a “bounce” occurs. We will explain the two main types that exist and how they affect your campaigns.

Definition and characteristics of soft bounce

A soft bounce represents a temporary delivery failure which occurs when your email reaches the server but bounces for temporary reasons. Remember that in these cases, the email will not appear in any of the recipient’s folders (inbox, promotions or spam).

We show you the most common causes of soft bounce:

• Full mailbox (over quota)
• Mail server temporarily out of service
• Message too large
• Content blocked by filters
• Relay problems between servers

Soft bounces are less damaging to your reputation. Email service providers (ESPs) will try to forward these messages for a certain amount of time. However, if the email keeps bouncing, it could become a hard bounce.

Definition and characteristics of hard bounce

The hard bounce indicates a permanent delivery failure. When it occurs, the email is definitely rejected and there is no possibility of future delivery. We recommend using an email validator to avoid these problems.

The main reasons for hard bounce are:

• Invalid or non-existent e-mail address
• Nonexistent or incorrect domain
• Mail server permanently blocked delivery
• Authentication problems (IP or blacklisted domain)

ESPs automatically block these addresses to protect your contact list.

Key differences between the two types of rebound

The fundamental difference lies in its permanence: while soft bounce is temporary and can be resolved, hard bounce is permanent and will not improve with resending.

Hard bounces severely damage your sender reputation. A high rate indicates problems in the hygiene of your contact list and can damage the reputation of your domain.

ESPs act differently with each type: they immediately delete addresses with hard bounce, while with soft bounce they perform several forwarding attempts before deleting them.

Common causes of soft bounce vs. hard bounce

Why do your emails bounce? Knowing the specific causes will help you implement effective solutions. We will explain the most common reasons and how to identify them correctly.

Temporary problems generating soft bounces

Soft bounces appear when your email arrives at the server but cannot be delivered for temporary reasons. Here are the most frequent causes:

• Recipient’s mailbox full (over quota)
• Server temporarily out of service or overloaded
• Message too large for the recipient’s mailbox
• Internet Service Provider (ISP) connectivity problems
• Content blocked by temporary spam filters
• Relay problems between mail servers

Remember that these problems usually resolve themselves. For example, a down server will be back up and running, or the user will empty their full mailbox.

Permanent errors behind hard bounces

When does a hard bounce occur? These indicate problems that will not be solved by more sending attempts. Here are the main causes:

• Invalid or non-existent e-mail address
• Invalid or non-existent mail domain
• Recipient’s mail server does not exist
• Permanent blocking by the receiving server
• Too many previous hard bounces that have damaged your reputation
• Rejection due to recipient server’s security policies

We recommend using an email verifier before running your campaigns to avoid these problems.

Examples of error messages for each type

Servers provide specific codes that help you identify the type of bounce. You will learn how to recognize them:

• 4XX codes: Signal soft bounces (temporary problems)
  • 421: “Service unavailable, transfer channel closing”.
  • 450: “Mail action not completed: mailbox not available”.
  • 452: “Requested action not completed: insufficient storage system”.
• Codes 5XX: Indicate hard bounces (permanent problems).
  • 550: “Requested action not completed: mailbox not found”.
  • 551: “User not local, please try another path”.
  • 553: “Action not allowed: mailbox not allowed”.

Impact of bounces on the sender’s reputation

Your sender reputation works just like a credit history in the world of email marketing. Email service providers (ESPs) and receiving servers evaluate every bounce that occurs on your mailings.

How hard bounces affect your sender score

Hard bounces immediately and severely damage your sender reputation. While soft bounces can be “forgiven” for being temporary, hard bounces reveal serious problems in your email marketing practices.

What happens when you repeatedly send emails to invalid addresses? ISPs interpret these actions as signs of bad practices, such as list buying or poor contact management. The result: your sender score decreases, reducing the likelihood of your emails reaching the inbox.

Remember that automatic systems detect patterns of hard bounces and start filtering all your mailings, even those addressed to valid addresses.

Consequences of a high bounce rate

We show you how a high bounce rate affects your strategy:

• Reduced deliverability: Your emails end up in spam folders.
• Shipping volume limitation: ESPs reduce your shipping capacity
• Possible blacklisting: permanent blocking of your domain or IP address
• Decrease in key metrics: Fewer openings and clicks
• Increased cost per acquisition: Resources lost on invalid contacts

Without proper follow-up, your messages will not reach potentially interested recipients.

Acceptable bounce limits according to the main ESPs

Our verification service recommends keeping the bounce rate below 2%. below 2%.. If you exceed this limit, you will need to immediately clean up your lists through a phone number and email validation.

What happens when certain thresholds are exceeded? Above 3%, you will receive warnings from suppliers. When you reach 5%, ESPs take severe measures:

• Temporary account suspension
• Deactivation of the registered sender
• Inability to make new shipments

A rate above 5% is considered critical and may result in permanent blacklisting of your domain.

Prevention strategies to reduce email bounces

Do you want to avoid bounces before they happen? Statistics show that a healthy rate should be kept below 2-5%. We’ll show you the most effective strategies to achieve this.

Implementation of an email validator for pre-testing

Pre-checking is your first line of defense against hard bounces. We recommend using an email checker before sending campaigns. This tool immediately detects invalid, non-existent or risky emails. For example, it identifies common errors such as “[email protected]” instead of “[email protected]”, significantly reducing permanent bounces.

Best practices for subscriber recruitment

Double opt-in guarantees quality lists. How does it work? When someone subscribes, they must confirm their address with a verification email.

Remember these additional recommendations:

• Beware of incentivized registrations – they often generate false addresses.
• Don’t buy mailing lists – they will inevitably increase your bounce rates.
• Ask your subscribers to update their data when they change their addresses

Regular maintenance of contact lists

The cleaning of your lists should be done every three months. Remove hard bounce addresses immediately to protect your reputation. You should also identify and delete contacts with no activity for more than 90 days – continuing to send them mailings can hurt your delivery rates.

Proper configuration of domain authentication

Proper authentication proves your legitimacy to the receiving servers. Configure these three main protocols:

• SPF (Sender Policy Framework): Authorizes servers to send from your domain.
• DKIM (DomainKeys Identified Mail): Ensures that your messages arrive unaltered.
• DMARC (Domain-based Message Authentication): Protects against identity theft.

We recommend sending from your own domain instead of free services such as Gmail or Yahoo. This practice significantly improves the deliverability of your campaigns.

Comparison Table

We show you the key differences between soft bounce and hard bounce. This table summarizes the most important points you need to know to effectively manage your email marketing campaigns.

Feature	Soft Bounce	Hard Bounce
Type of failure	Temporary	Permanent
Nature of the problem	Recoverable	Not recoverable
Main causes	– Mailbox full – Server temporarily out of service – Message too large – Relay problems between servers	– Nonexistent mail address – Nonexistent domain – Permanent server crash – Authentication problems
Error codes	4XX (421, 450, 452)	5XX (550, 551, 553)
Reputational impact	Minor impact	Severe and immediate impact
ESP handling	Multiple forwarding attempts	Immediate address deletion
Acceptable limit	Part of the total 2% allowed	Not to exceed 3%.
Action required	Monitor and wait	Immediate contact elimination

Remember that these parameters are essential to maintain a good reputation as a sender. Use them as a guide to identify and resolve problems in your emailing.

Conclusion

Email bounces are vital signals that indicate the health of your marketing campaigns. We recommend keeping bounce rates below 2% through a strategy that combines prevention and constant monitoring.

Why is it so important? Hard bounces demand your immediate attention because of their severe impact on the sender’s reputation. To protect your reputation, it is critical to implement robust checks before every mass mailing. Our email verification API automates this critical process, helping you maintain clean and up-to-date contact lists.

Remember that the quality of your data determines the success of your campaigns. While soft bounces are less serious, they need to be monitored for problematic patterns. Proper domain authentication, along with ethical subscriber acquisition practices, will protect you against both types of bounces.

Don’t forget that every bounce represents a lost contact with your audience. Proactive prevention, through specialized tools and defined strategies, ensures the effective delivery of your messages. If you have questions about how to implement these practices, our support team will be happy to help you maximize the return on your email marketing campaigns.

FAQs

Q1. What is the main difference between a soft bounce and a hard bounce?
A soft bounce is a temporary failure in mail delivery, such as a full mailbox, while a hard bounce is a permanent failure, usually due to an invalid email address or a non-existent domain.

Q2. How do bounces affect the sender’s reputation?
Bounces, especially hard bounces, can severely damage a sender’s reputation. A bounce rate above 3% can result in blacklisting and negatively affect the deliverability of future mailings.

Q3. What strategies can I implement to reduce email bounces?
Using an email validator before sending campaigns, implementing a double opt-in process for new subscribers, regularly maintaining contact lists and correctly configuring domain authentication are effective strategies to reduce bounces.

Q4. What is the acceptable bounce rate in email marketing?
It is recommended to keep the total bounce rate below 2%. A rate above 5% is considered critical and may result in penalties from email service providers.

Q5. Should I immediately remove the addresses that generate hard bounces?
Yes, it is advisable to immediately remove addresses that generate hard bounces from your list. This helps to maintain a clean contact list and protects your reputation as a sender, avoiding deliverability problems in future campaigns.

Q6. Is there a verification solution to avoid bounces in SMS campaigns?
Yes, if you are using a multi-channel strategy for sending voice or sMS campaigns, we recommend validating phone numbers before sending the campaigns to avoid hard bounces and if you want to automate the whole process you can use the validate phone api.