Bounce Email Analytics: Diagnose and Fix the Issues Impacting your Deliverability

Track Bounce Emails

There is no email marketer that has never received bounced emails. Sooner or later bounced emails happen even if you have the cleanest list possible.

From one side, bounce emails are a nasty thing because they negatively influence your sender reputation and deliverability.

From the other side, they do a good job by giving you a plenty of information about the quality of your mailing list, recipient engagement, and your email campaign performance.

In order to improve email conversions, you need to understand what bounce emails tell you in order to determine and address the issues.

With the right tool like GlockApps Bounce Monitor, you can receive advanced bounce email analytics for each sender, provider, bounce type, and reason, and quickly find out the weak sides of your email program.

For bounce email tracking, the GlockApps Bounce Monitor is integrated with Amazon SES, SendGrid, SparkPost, and Mailgun delivery services.

You can also connect to your IMAP server from the GlockApps Bounce Monitor to track bounce emails.

Below I tell you how GlockApps Bounce Monitor helps you diagnose and fix the issues impacting your sender reputation and deliverability.

What is Bounced Email?

Bounced email is an email that could not be delivered to the recipient’s mailing address and was returned to the sender.

Often people mistakenly think that bounce occurs due to miscommunication with the client’s server. In reality, email bounces after it is accepted by the recipient’s server, but could not be delivered to the email address due to one of several reasons.

The percentage of the bounced emails to the overall amount of messages sent is called the bounce rate. The average acceptable bounce rate may vary for different ESPs, but your messages can be blocked if it exceeds 10%.

The bounce rate should be tracked regularly to avoid a negative influence on the deliverability rate.

Finding Bounce Peaks

You can start by examining general statistics about bounces in your Bounce Monitor Dashboard.

Select the period, for example, the last 7 days, and look at the diagram.

See if there are peak lifts of any type of bounce emails. Hover the mouse over a particular day to see the bounce statistics for that day.

Look at the data below the diagram to find out how the numbers increased or decreased in comparison with the previous 7-day period or whatever interval you choose.

As the picture below shows, we observed an incredible lift of dropped and soft bounce messages during the chosen 7-day period.

To dig deeper, click on the “View Reason” button to get bounce email analytics by providers and bounce reasons.

GlockApps Bounce Email Analytics Dashboard
Bounce Email Analytics

Investigating Bounce Reasons

When you send an email and a mailbox provider at the receiving side cannot accept it, it will respond with a message (bounce reason) and a code.

The GlockApps Bounce Monitor normalizes the bounce data, sorts it out, and provides comprehensive analytics which show by priority the items that are most frequent and need attention.

Thus, you can look which providers generated the highest numbers of bounce messages and what their reasons are: blocked sender, spam content, SPF, deferred emails, full mailbox or other.

Different bounce reasons indicate different problems and require different approaches to fixing them.

Some of the reasons for a “blocked sender” bounce are: the sending IP or domain is blacklisted, the sender email address is rejected, the receiving server immediately drops the connection, there are too many connections from the IP address.

The “spam content” reason speaks for itself: the message content did not pass through the anti-spam filters set up on a mailbox provider and was returned to the sender.

Bounce emails with the “SPF” reason let you know that something is not good with your SPF record. You’ll want to check your DNS settings and verify your SPF record.

The “mailbox full” is either a permanent error telling you that the recipient’s mailbox is over quota or a temporary error indicating a temporary delivery failure.

Deferred emails tell you that the receiving mailbox provider has temporarily limited access to their system and put your email into a queue.

It could be because their servers are too busy right now. It could be because the mailbox provider is seeing too many spam complaints about your email that has already been delivered. It could be because you are a new sender and they are cautious. It could be because the receiving server is throttling emails from the given IP address or you reached the limit of emails that can be received by the given account. You never know without looking into the details.

In our case, we had 1,800,000+ deferred emails for the G Suite provider.

GlockApps Bounce Email Analytics by Bounce Reason
Bounce Email Analytics

To view the detailed information about diagnostic codes with the bounce description, click on the number in the appropriate column.

In our case, we examined the deferred emails for G Suite and found out that most of them had the below bounce reason:

450 4.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional
messages from being delivered. Please resend your message at a later time. If the user is able
to receive mail at that time, your message will be delivered. For more information, please visit h30si2464644qtc.231 - gsmtp

It let us know that too many messages had been sent to the email addresses set up with G Suite and the receiving quota had been exceeded.

If the “View” link is active, you can click it and read how to fix the issue. GlockApps Bounce Monitor tries to gather as much information from bounce emails as possible to give you the complete report and suggest a solution.

GlockApps Bounce Email Analytics by Diagnostic Codes
Bounce Email Analytics

What we need to do about deferred emails is to identify the email addresses in question and exclude them from email campaigns in our mailing software.

To see the email addresses, click on the number in the “Count” column.

You will get the list of email addresses that bounced for the given reason.

Investigating Bounce Types

Another good thing is to examine bounce email analytics by the bounce types.

Click the arrow next to “Reasons” on the top and select “Types”.

GlockApps Bounce Email Analytics: Deferred Bounces
Bounce Email Analytics

The GlockApps Bounce Monitor gives the breakdown of bounces by the bounce type and provider in order you can easily see where the problem lays.

We differentiate bounce emails by the following types:

HARD – messages that bounced because of invalid email addresses to which the delivery permanently failed

SOFT – messages that bounced because the delivery temporarily failed

BLOCK – messages that bounced because the sender or content is blocked by the receiving server

FBL – email notifications sent after a recipient reports a spam complaint

DROPPED – messages that have been prevented from being delivered by the sending system due to some past issue with the email address: the email address doesn’t exist, the domain is not set up to receive emails or the recipient marked previous messages as spam.

Email service providers do this to protect their sending reputation with ISPs and ensure reliable delivery for all their customers.

UNSUBSCRIBE – unsubscribe requests from the recipients

The picture below demonstrates that we had a high number of dropped emails during the last 7 days.

GlockApps Bounce Email Analytics by Bounce Type
Bounce Email Analytics

To see the email addresses for dropped messages, I click the number in the “Dropped” column.

GlockApps Bounce Email Analytics: Dropped Bounces
Bounce Email Analytics

Our report shows that a lot of dropped messages result from one invalid email address. We need to suppress all email addresses under the Dropped Bounces report from our mailing list.

Why Suppress Dropped Bounces?

While “dropped” email addresses exist on your list, they eat your sending quota and money.

Although your email service provider prevents the message delivery to “dropped” email addresses on its side, they still count the messages sent to those addresses and charge you for each message sent to “dropped” emails.

In our example, we had 120,440 dropped bounces within 7 days. You can estimate the price you would pay to your ESP for 120,440 “dropped” emails yourself.

How to Export Bounced Emails?

The export option in the GlockApps Bounce Monitor is very flexible and allows you to choose the bounce types and fields for export.

Go to the Bounce Monitor -> Export menu item in your account dashboard.

Choose the bounce type, for example, Dropped Bounce, and the fields, for example, Bounce Email.

Click “Export”.

GlockApps Bounce Monitor: Export Bounced Emails
Bounce Email Analytics

In the output CSV file, the bounce type is presented as a number which corresponds to the following bounce types:

1 – hard bounce
2 – soft bounce
5 – blocked
9 – unsubscribe
15 – abuse (spam complaint)
20 – dropped

Suppress exported email addresses from your mailing list.

You also need to suppress hard bounce, FBL and unsubscribed emails from your mailing list. If you keep sending to those users, it is bad for your sender reputation.

Soft bounce and blocked emails should be analyzed and addressed too. If soft bounces happen because the messages are deferred, you should send less or temporarily stop sending to soft bounce email address.

For blocked emails, see the blocking reason and fix it.

How to Receive Alerts about Bounced Emails

The Bounce Monitor can send you email alerts when the number of bounce emails reaches or exceeds the values specified by you. It helps you identify the peaks of bounce emails and understand which email campaigns generated the highest bounce rate.

A lot of delivery services will suspend the user’s account if the bounce rate exceeds the threshold (the industry average value is 10%). With the Bounce Monitor alerts, you will be proactively informed when the quantity of your bounce messages is reaching the allowed threshold.

You can activate the sending of the alerts in the Bounce Monitor Settings.

Fill in the fields:

Alert email – enter the email address to receive the alerts.

Alert interval – choose the interval to send email alerts (from 5 minutes to 24 hours)

Be aware that if you set a short interval when receiving a high number of bounce emails, you will be getting a lot of email alerts from the GlockApps Bounce Monitor.

Check the boxes next to the bounce types you want to receive alerts about and enter the number of bounce messages to be used as the control value.

Click Save.

The alert will be sent when the number of bounce emails of the selected types reaches or exceeds the control value within the chosen alert interval.

Bounce Email Alerts

Ways to Reduce Your Email Bounce Rate

Follow these best practices to reduce bounce rate and keep your deliverability high:

  1. Authenticate Email

    Cyber-security is a big issue in the 21st century, so make sure you have SPF, DKIM, and DMARC protocols implemented on your domain.

  2. Maintain a healthy email list

    Never use purchased email lists to avoid spam traps and blacklisting; use double opt-ins to ensure your subscribers agreed to receive your messages; provide an unsubscribe rate; keep email list up to date.

  3. Make email send-outs scheduled and consistent

    People tend to change or abandon their email addresses. If you don’t send emails for some time, the next thing to happen is a spike in bounce rates because by that time your email list will accumulate many abandoned addresses.

  4. Be careful with the content

    If your content resembles a spam message it will not reach your recipient. Be cautious about what you write in the letter as well as the subject line. Spam filtering advances all the time, so keep an eye on these changes.

  5. Monitor your deliverability and performance regularly

    Use Bounce Tracker to see bounce rates, determine reasons for a bounce, and receive guidelines to resolve issues.

Closing Thoughts:

It is important that you have a tool that gives you advanced bounce email analytics in addition to only excluding hard bounces from your mailing list.

Having good bounce analytics allows you to track your email campaign performance over time and identify problem campaigns, senders and providers in order you could address the issues.

In particular, with the GlockApps Bounce Monitor you can find the answers to these questions:

  • Do I need to clean my list from invalid addresses?
  • Do I send relevant messages?
  • Does any provider block my emails and why?
  • Is my IP blacklisted?
  • How do I fix the issues?

With the right data, you get a clear picture of what is going on after you hit the Send button and understanding of what to do to avoid deliverability issues in the future.


Julia Gulevich is an email marketing expert and customer support professional at GlockSoft LLC with more than 15 years of experience. Author of numerous blog posts, publications, and articles about email marketing and deliverability.