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The Quick Guide to Bounce Codes & Email Deliverability
Contained: Everything you need to know about
the Postmaster & Mailer Daemon
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.
Why Care About Bounce Codes?
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.
Before talking about bounce codes, 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.
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.
Use Clean, Verified 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.
Polish Your Segmentation & Add 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.
Avoid 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? |
Is There 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.
Understanding the Various 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
Compiled 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 on Bounce Codes
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!
Monica Marino
Director of Customer Success
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