The Quick Guide to Bounce Codes and Email Deliverability

Monica Marino, Director of Customer Engagement

Why Care About Bounce Codes?

As an outbound sales rep there is nothing more frustrating than finding out your emails were undeliverable. This is especially true after spending (wasting) time on research and preparation only to see an automated reply from the Postmaster or your least favorite friend, Mailer Daemon.

Prospecting takes time, and time is money. This guide it’s essential for you to understand why your emails aren’t making it to your prospects’ inbox.

Let’s begin by defining what is a bounced email.

Simply put, a bounce message is an automated reply from the prospect’s email server notifying you that the email was not delivered.

In outbound sales, delivery correlates directly with replies. Replies correlate with conversions. And with conversions directly linking to pipeline and hitting quota, you could say that it’s kind of a big deal to lower bounce rates. If you need more of a reason to worry about it, consider that bounced emails negatively affect your IP reputation. This correlates to how emails get blocked, flagged, or blacklisted.

Let’s talk about what you can do to monitor your email address.

Check your spam score. This is a numerical rating (0-10) that takes several elements into account. There are two primary ways emails can get blocked. The first is automatic email filters and the second is an email being manually marked by the recipient as spam. Both affects your spam score. So a good place to start is to use free sites available like https://www.mail-tester.com/ to understand if your emails are at risk.

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Understanding Two Types of Bounces

Soft bounces versus hard bounces are the two categories of bounce messages. A soft bounce (which starts with a “4xx”) which in most cases can be fixed doesn’t affect your spam score as much as a hard bounce. This is why it’s important for outbound sales reps to use reputable data sources to maximize deliverability. In today’s day and age, employees change jobs more frequently, which means an increase in data degradation that currently averages to 24-36%. That means that ¼ of your email will hard bounce due to bad data.

So What are the Differences?

A soft bounce is a temporary issue related to the prospect’s server. The email address may be unavailable or full. The prospect’s server could have insufficient storage or issues processing the delivery. The good thing with soft bounces is that they will eventually be fixed. But be patient because five consecutive undeliverable attempts will turn to a hard bounce.

On the flip side, a hard bounce (starting a with a “5xx”) will never turn into a soft bounce. These errors are permanent and cannot be fixed.

Nevertheless, some email deliverability errors are in your control and others are not. So let’s dig into common reasons why emails bounce that are in your control.

Good & Clean Data

Data degradation is at an all time high, so don’t use unreliable contact lists. Buying lead lists is dead. Successful sales teams use sales automation tools that provide verified email addresses. In most cases this is done by using a browser extension that computes the email addresses using an internally built algorithm.
Scrub your list to remove incorrect or old emails which affect bounce rate and your spam score. Sales automation tools can provide the validity of the email addresses so you can remove all invalid emails.

Segmentation & Personalization

Understand your company’s buying personas and the target market. This can prevent your emails from being manually marked as spam if the emails are being sent to the wrong audience.
Test catchy, unique, short and sweet subject lines. Also try A/B testing messaging. If you aren’t, you are losing the opportunity to understand what works and what doesn’t to increase open rates and reply rates.
Ask yourself if the prospect’s pain points are addressed clearly and concisely. If they are not, edit the message because the goal of personalization is to have the data points resonate. Sales enablement tools like FoxBound can make this process seamless. And the more unique the message, the less likely your email will be sent to spam.

Spam Filters Triggered by your Email Content:

Keep the exclamation points to a minimum. This is one example of many triggers that Google and Outlook are looking for to block emails that are likely to be spam.
Use standard formats and fonts. This includes capital letters and crazy colors if you want your email to reach the prospect
Compress images and check your image to text ratio. Spam filters look for large embedding image. It is also recommended that an email should consist of about 70% text and 30% images to avoid filters.
Remove excessive links. Emails will be flagged and sent to spam if the text contains more than six links.
Review the text to avoid common spam words that are blocked in subject lines and in the body of an email.

Spam Words & Phrases

Here’s a list of words and phrases to steer away from, especially within subject lints.

% off	Click here	Get started now	New customers only	Reverse
$$	Compare rates	Great offer	No gimmicks	Risk free
100% free	Credit	Guaranteed	No investment	Sample
100% satisfied	Don’t delete	Help	Now only	Satisfaction
Acceptable	Don’t hesitate	Hidden	Obligation	Search listing
Accordingly	Double your	Hidden costs	Offer expires	See for yourself
Act Now	Double your income	Increase sales	One time	Serious cash
Affordable	Drastically reduce	Increase traffic	Opportunity	Shopper
Apply now	Earn $	Incredible deal	Order	Special promotion
Avoid	Earn extra cash	Info you requested	Order Now	Stop
Beneficiary	Expect to earn	Instant	Order today	Supply is limited
Best price	Explode your business	It’s effective	Please read	Test
Billion	Extra income	Lifetime	Potential earnings	Thousands
Can’t live without	Extra income	Limited time offer	Prices	Time limited
Cash bonus	F r e e	Lose	Problem	Trial
Certified	Fantastic deal	Maintained	Promise you	Urgent
Chance	Fast cash	Make $	Real thing	Visit our website
Cheap	For you	Medium	Refinance	Web traffic
Claims	Free	Miracle	Reminder	While you sleep
Clearance	Full refund	Never	Remove	Why pay more?

What is an Acceptable Bounce Rate?

There are some factors out of your control. Even if you do everything in your power to follow the guidelines above to ensure emails are received and your messaging resonates with your audience. That said, note that an acceptable bounce rate is between 2-5%. Anything over 5% suggests a significant problem that you will want to resolve.

Formats of Bounce Codes

It’s important to understand bounce codes to solve delivery problems. The traditional SMTP bounce reasons are three-digit codes (550), and the enhanced SMTP bounce responses are three-digits separated by decimal points (5.1.1). to see a list of error codes with a brief explanation

Bounce Codes Errors with Explanations

Bounce Code	Type	Explanation
250		Mail accepted by receiving network
421	Soft	Message was temporarily deferred by the recipient server as a result of too many connections in a short timeframe or too many messages.
450	Soft	Requested mail action not taken: mailbox unavailable
451	Soft	Requested action aborted: error in processing
452	Soft	Requested action not taken: insufficient system storage
500	Hard	The server could not recognize the command due to a syntax error.
501	Hard	A syntax error was encountered in command arguments.
502	Hard	This command is not implemented.
503	Hard	The server has encountered a bad sequence of commands.
504	Hard	A command parameter is not implemented.
550	Hard	User’s mailbox was unavailable (such as not found)
551	Hard	The recipient is not local to the server.
552	Hard	The action was aborted due to exceeded storage allocation.
553	Hard	The command was aborted because the mailbox name is invalid.
554	Hard	The transaction failed for some unstated reason.
4.2.2	Soft	The email account is over quota
5.0.0	Hard	Address does not exist
5.1.0	Hard	Other address status
5.1.1	Hard	Bad destination mailbox address
5.1.2	Hard	Bad destination system address
5.1.3	Hard	Bad destination mailbox address syntax
5.1.4	Hard	Destination mailbox address ambiguous
5.1.5	Hard	Destination mailbox address valid
5.1.6	Hard	Mailbox has moved
5.1.7	Hard	Bad sender’s mailbox address syntax
5.1.8	Hard	Bad sender’s system address
5.2.0	Soft	Other or undefined mailbox status
5.2.1	Soft	Mailbox disabled, not accepting messages
5.2.2	Soft	Mailbox full
5.2.3	Hard	Message length exceeds administrative limit.
5.2.4	Hard	Mailing list expansion problem
5.3.0	Hard	Other or undefined mail system status
5.3.1	Soft	Mail system full
5.3.2	Hard	System not accepting network messages
5.3.3	Hard	System not capable of selected features
5.3.4	Hard	Message too big for system
5.4.0	Hard	Other or undefined network or routing status
5.4.1	Hard	No answer from host
5.4.2	Hard	Bad connection
5.4.3	Hard	Routing server failure
5.4.4	Hard	Unable to route
5.4.5	Soft	Network congestion
5.4.6	Hard	Routing loop detected
5.4.7	Hard	Delivery time expired
5.5.0	Hard	Other or undefined protocol status
5.5.1	Hard	Invalid command
5.5.2	Hard	Syntax error
5.5.3	Soft	Too many recipients
5.5.4	Hard	Invalid command arguments
5.5.5	Hard	Wrong protocol version
5.6.0	Hard	Other or undefined media error
5.6.1	Hard	Media not supported
5.6.2	Hard	Conversion required and prohibited
5.6.3	Hard	Conversion required but not supported
5.6.4	Hard	Conversion with loss performed
5.6.5	Hard	Conversion failed
5.7.0	Hard	Other or undefined security status
5.7.1	Hard	Delivery not authorized, message refused
5.7.2	Hard	Mailing list expansion prohibited
5.7.3	Hard	Security conversion required but not possible
5.7.4	Hard	Security features not supported
5.7.5	Hard	Cryptographic failure
5.7.6	Hard	Cryptographic algorithm not supported
5.7.7	Hard	Message integrity failure
9.1.1	Hard	Hard bounce with no bounce code found (invalid email, rejected email from your mail server such as from a sending limit)

Conclusion

At the end of the. day, it’s not difficult to prevent your emails from getting blocked and marked at spam. The most overlooked step is to ensure that your company is using a trusted data source that can provide quality email addresses, and the rest is on the sales rep to follow the basic guidelines highlighted above.

And when you exceed quota by making these quick changes to your outbound process, don’t forget to share this guide with a friend. Happy hunting!

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September 17, 2019