Email Bounce Back Decoded: 8 Ways to Reduce your Email Bounce Rate
Written by
Tejas Pitkar
Tejas Pitkar

Subscribe for updates

Email Bounce Back Decoded: 8 Ways to Reduce your Email Bounce Rate

Published : May 4, 2020

This article talks about one of the major issues which has been with us since the advent of emails – Email Bounce Back. We have tried to throw light on concepts which are as basic as What is Email Bounce Back to the reasons of Email Bounce and how can you avoid them!

So as a Brand Marketer, you did all the hard work to send your latest promotions to your email subscribers.

You created an attractive Email campaign and decide to send it to your mailing list for your Friday sale. The engagement column is showing increasing open rates and you are delighted!

But then you realize the column for “Bounces” is increasing as well and is showing red!

A little digging deep and you come to the conclusion that these are the users who have not been delivered your Email due to some reasons. You check the logs for the Emails sent and you receive a bunch of confusing error codes from Mailbox providers stating why they could not deliver your Emails.

It is incredibly frustrating for a Marketer to go through the phenomenon called “Email Bounceback”. Soon you come to the stark reality that your mailing list contains email ids that are not valid and cannot be mailed to. Also, if you continue to mail them, it will bring down your IP reputation and Inboxing, affecting your overall Email Program.

How exasperating for a Marketer!!!!

Fig: That’s every frustrated Marketer meditating post bounces.

What do you mean by Email Bounce back?

When your sent Email is rejected by recipient mail server then, it gets bounced back to your server. This is called a bounced Email. The email could not be delivered to the recipient mailbox due to some reason – which will be stated in the bounce code in the error message received on your server.

Every Mailbox provider have their own SMTP bounce codes which state the reasons for the undelivered email.

A high Email Bounce rate affects your deliverability in a negative way. Hence you need to keep those bounce-back rates low to improve your Email Deliverability.

Your Email Bounces could tell you a lot more about your Email database and deliverability. So use it to gain more knowledge about your mailing list and try to reduce them for the next campaign.

And if you wish to do exactly that, then you are in luck at Pepipost.

In this definitive guide to Email Bounce-back, we shall be covering in-depth the following:

  • Why do Emails bounce?
  • What are the types of Email bounces?
  • How do bounces affect your email deliverability?
  • How to reduce Bounces and clean your lists?

According to Master Shifu – Time is an illusion and there is only the NOW.

So we are here to help you master Email Bounce-backs like a Master!

So let’s start the journey of enlightenment… What are Soft and Hard Bounces?

It’s common when your Email bounces back because the recipient’s inbox is full, or the recipient server is down. Either, the email you are sending is too large for the server load or your attachments are too big in size to deliver.

These kinds of bounces are called Soft Bounces. They are called Soft Bounces as they are temporary. These emails can be delivered with some changes or when the mailbox of the recipient has space.

Hard Bounce is an Email that cannot be delivered as it has been rejected by the recipient server owing to blacklisting of the IP address or because the email id you are sending the mails to is not valid and does not exist.

It is recommended that you do not persevere in sending these emails to the same recipients, as they could affect your IP black-listing by Mailbox providers and in turn, your Inboxing could also face issues.

Ideally, the Email id which has got hard bounced, as it is invalid, should be blacklisted by your ESP and not delivered again.

Hard Bounces are looked at by Mailbox providers as a serious issue and if continued are punished by severe deliverability and IP listing issues. It is better to clean your Email list and determine what Email ids are active and need to be targeted before sending the Email campaign.

Why do Emails Bounce back?

So how do Emails bounce after all?

We have presented 8 common reasons why your Emails may bounce in the below guide…

1. Invalid Email ids

It is very often that we find this error from the receiving server as it bounces the mail back to your mailing server.

This happens when a certain email address you tried to send mail, did not exist or was invalid.

It is also possible that the person does not have a valid email address or there has been some typo mistake in providing the correct email address.

In case of corporate ids, this could mean an individual who left the organization and their email id is no more valid.

Sometimes in a marketer’s mailing list, you will find email ids collected off the website where there is no email validation. In such cases, users might also provide fake or unauthentic email ids.

Such email addresses will bounce back to your server as these are not having valid mailboxes.

Example error code for Gmail:
550, “5.1.1”, The email account that you tried to reach does not exist. Please try double-checking the recipient’s email address for typos or unnecessary spaces.

2. Mail not delivered:

Mails may not be delivered to the intended recipient server as there could be issues with the server storage allocation or the server may not be functioning appropriately. Sometimes the recipient mail servers are surrendered by the organization to other sources for usage.

In some cases the server may not be available for delivery as it could have stopped functioning.

In such cases the mails won’t be delivered and will be bounced back to your delivery server.

Example Error code:
451, “4.3.0”, Mail server temporarily rejected message.

3. Full Mailbox:

There are a lot of emails that a user might receive from all the websites they have subscribed to, or sometimes even when they have not subscribed aka spam emails 😉

A mailbox will have a limited storage ability to store emails. This might become full and hence there will be no space for another incoming email. In such cases, the mailbox provider will bounce the email back to the delivery server.

As such these emails could be tried again to be delivered later when the recipient mailbox will have the space to store them.

Example Error code:
552, “5.2.2”, The email account that you tried to reach is over quota.

4. Emails getting blocked:

Some recipient servers like corporate servers only allow certain IP addresses to deliver emails to the intended recipient. In such cases, the other IP addresses trying to deliver emails will be blocked.

These emails will be bounced back as the mails are not allowed to deliver to this server. In such cases, you have to whitelist the IP address which you need to deliver the emails. This IP address can belong to a certain delivery server from an organization or an ESP (Email service provider).

There are many times a server administrator in an organization might blacklist the IP address which is delivering the emails, in case the IP address have not been whitelisted to deliver emails to the recipient server. The emails will thus be blocked and bounce back.

Example Error code:
550, “5.7.1”, Our system has detected an unusual rate of unsolicited mail originating from your IP address. To protect our users from spam, mail sent from your IP address has been blocked.

5. Blacklisted IP address :

A lot depends on your delivery IP reputation. If the sender score of these IPs is low and they have been used in the past for sending spam emails then these IPs may get blacklisted by Mailbox providers. If the IP is blacklisted by a mailbox provider then it can get blocked. Thus, emails sent by blacklisted IPs will bounce and won’t be able to deliver.

Example Error code:
421, “4.7.0”, Our system has detected an unusual rate of unsolicited mail originating from your IP address. To protect our users from spam, mail sent from your IP address has been temporarily blocked.

6. Too many hops and large message size:

Sometimes the number of server hops that an outgoing mail has to take exceeds the limit set by a recipient server hence due to the mail looping around several servers in the network, the message cannot be delivered.

Example Error code:
554, “5.6.0”, Message exceeded 50 hops, this may indicate a mail loop.

There are also instances when the message size exceeds the normal limit of attachments of say 25MB then the mails will not be accepted by the recipient server and they bounce-back.

Example Error code:
552, “5.2.3”, Your message exceeded Google’s message size limits.

7. Auto Responder

These emails have an auto-reply or auto-responder on, for someone who has been on leave or vacation.

If you send an email to this person, then your mail will soft bounce and will be later delivered when the person has disabled the autoresponder.

8. Others

Apart from the above, there is a multitude of reasons why your emails could bounce.

There could be issues with the local recipient server or the mailbox provider might not allow any delivery for the email ids for the present time.

We can get to know more about these from our SMTP error codes.

Some Mailbox specific SMTP error codes are as follows:

Gmail SMTP Error code:
Yahoo SMTP Error code:

Microsoft Outlook SMTP Error code:

How do Email Bounce-backs harm your Email Deliverability?

Deliverability in layman terms is “the rate at which your emails land in the user’s inbox folder and not in spam folder”.

If you are sending emails to invalid ids or for some or the other reason your Emails are hard bouncing and you continue to keep sending to these ids then there is an avalanche of deliverability issues coming towards you.

Firstly, your IP reputation will take a dip if your hard bounce percentage is higher than 5% on a regular basis. More hard bounces indicate suspicious bulk emailing to MSPs which can severely dent your IP address capability to deliver those emails.

Also, the emails which are hard bounced can get you into trouble with major anti-spam authorities like DNSBL, Spamhaus, etc. If your emails are permanently deferred then you may have to white list your IP with those mailbox providers or anti-spam authorities until it is to be used again. This process can take a longer time.

The biggest impact perhaps that your hard bounces will have on your Email Program will be on your deliverability.

Email Deliverability takes a serious hit when your hard bounce percentage is near the region of 5% plus on a regular basis. Sooner or later, you will see large valleys in your inboxing graph. Domain reputation which is an indicator of the MSP of your domain hygiene is downgraded when you receive hard bounces on your sent emails.

The way you calculate your bounce percentage is:

( total bounces received / total sent mails) * 100

Thus hard bounces can destroy all the good work you might have done with your Email program before, in a matter of a few days. Receiving Email Bounce-backs sets a bad precedent for handling and scanning your emails for an MSP.

Soft Bounces, on the other hand, do not harm your Inboxing but are yet red flags for a deliverability Engineer to check their mailing list and mail to those email ids which have authentic email ids and are active on email.

If you get a bounce error code saying “the recipient mailbox is free” then you should avoid targeting the same mailbox for some period of time before initiating again.

‘An acceptable Email Bounce rate is somewhere between 2-5%. If your campaigns receive regular bounces above 5% then it can be detrimental to your Email Deliverability.’

In such cases, you will need to find the issue behind the bounces and rectify it immediately or else your Email Inboxing will go for a toss.

So how do you Improve on your Bounce-Back rate?

So now let’s have a look at how you can reduce that Bounce rate and get back in the good books of Mailbox Providers:

1. Prioritize double opt-in email collection

If you wish to reduce email bounces, you will have to prioritize and analyse the way you collect email ids from your subscribers visiting your website.

When a user is subscribing to your Email Newsletter with their email id, are you sending them a confirmation email to verify their subscription? This email is triggered within 2 minutes of the action of user entering their email id and subscribing.

When the user confirms their opt-in on their entered email address then the subscription is verified.
This is called double-opt in verification.

This method ensures that your mailing list will contain authentic email users who have signed up and confirmed their credentials on mail. Mailing to such valid user ids will firstly lead to good engagement for your newsletters and will reduce your email bounces.

Maybe they might reduce the amount of users you receive due to the opt-in process involved but it will guarantee a sweet return on your mailing performance if you mail only to verified email ids.

2. Have a healthy sunset policy to phase out inactive users:

Your mailing list won’t remain the same always. Some email users might decide to unsubscribe or they might get disinterested with your promotional communication.

If you are not carefully monitoring the engagement performance of your campaigns, you could potentially end up with inactive users being mailed to on a regular basis. These inactive users are not checking your mails and not unsubscribing either due to some reasons.

The way major mailbox providers like Gmail and Yahoo have updated their algorithms is to ensure that only those emails are received by users who are actually engaged with the brand.

Hence if half of your list is not responding to your mails then eventually after say 60-90 days of inactivity, those users will start receiving their emails in spam automatically.

Hence it is recommended to apply an effective Sunset Policy to your mailing list. If you see users not engaging with your mails after a 60-90 days period then remove them from their mailing list and say goodbye. This will reduce a user from your list, but it will also ensure that your email inboxing remains high as you are mailing only to users who are engaging with your newsletters.

So it is time to say goodbye to some email ids.

3. Avoid purchasing Email Lists

Purchased email lists contain email users who haven’t subscribed to your website.

Mailing to this unsuspecting user list will get you a high number of unsubscribes and report to spam complaints.

These lists will also have website scratched or crawled data which contain invalid ids. These will result in a high hard bounce rate giving a negative indication to Mailbox providers, of spamming or unethical mailing activity.

Thus, avoid using purchased lists as part of your mailing strategy.

4. Avoid Random Mailing Pattern

Another trust killer of mailbox providers. Any random or unpredictable mailing will lead to high volumes being sent in a shorter period of time.

When you send a high volume of mails, and if your usual volumes are lower then the server admins of mailbox providers will block your mails. Your ip addresses could be placed in suspicious list or even blacklisted by anti-spam authorities.

Thus, it is wise to keep a regular pattern of mailing and not send any ad-hoc type communication which could dissuade the mailbox servers from receiving your emails. Such random mailing pattern will also lead to a dip in your email deliverability.

This would avoid any blocks from MSP (Mailbox Service Provider) side and reduce chances of having hard bounces affect your Email Program.

5. Clean your list before using it

If you are a brand Marketer and if you have a list of email ids that you have received from your CRM system then there are chances that there could be invalid ids or typos in the spelling of the email addresses. This could mean that some percentage of the list will need to be cleaned before usage.

You should make sure that you manually check the list of ids and figure out any invalid ids or possible spam traps in it. If there are any typos in the email ids then they need to be fixed for them to be included in the mailing list. If they can’t be verified then it is best to leave them out.

List hygiene is an important part to get right for every Email Program to succeed. The cleaner your list, the better will be your engagement as you can reach out to all your users.

6. Avoid Sending Spam Content

Spam content could comprise of spammy subject lines, spam or hidden content in the body of the HTML. It could also mean misleading subject lines and irrelevant content.

Also if the size of the mailer is large then the MSPs could reject the delivery and your emails will bounce as a result.

7. Monitor your complaints and abuses metrics

If you keep a lookout for a number of abuse complaints you get for your campaigns and the number of reports to spam complaints on Google Postmaster, you will have a clear idea of how the users are responding to your campaigns.

And if you are receiving abuses from users on Yahoo, reduce the frequency of mailing to these users. If the percentage of the report to spam complaints on Gmail is greater than 0.2% on a regular basis then you have to look at the messaging you are directing to your subscribers.

If restorative actions are taken on time then MSPs would stop blocking your emails due to user abuse complaints and will help to improve your bounce rate.

8. Monitor your IP Reputation

The IP addresses that you use to deliver the mails to recipient servers need to carry a good reputation with MSPs to be allowed to deliver mails on a consistent basis.

With Yahoo, you have to build your sender score and with Gmail you have to build your IP reputation and monitor it on Postmaster tool.

If you have been sending spam content or receiving a lot of abuse complaints from users, but have not taken any action to rectify the issue then it might come back to haunt you.

If your IP addresses are having poor reputation, then your mails can get deferred and eventually blocked by MSP server adminstrators. This will result in high bounces and will lead to an inability to send emails from that IP address for a period of time.

This could lead to a revenue loss as you won’t be able to reach out to your potential customers.

So it is prudent to keep your Email Program in equipoise and monitor your Ips and how they are performing.

Wrapping up

Thus we have seen what causes Email Bounce-backs and what a Marketer needs to do to reduce on the bounce rate to deliver your emails to genuine subscribers.

We would suggest looking at Email Bounce backs as if its a path correction course rather than an obstacle.

If you follow the above guide then you will definitely improve on your bounce rate and not succumb to the disaster that happens when you don’t monitor vital metrics of your campaigns.

It all comes down to creating a hygienic Email list and churn away inactive users from time to time. Also scrub your list before usage and mail only to valid users.

If you have any other techniques to keep those Email Bounces to a minimum then let us know in the comments below!

Unlock unmatched customer experiences,
get started now
Let us show you what's possible with Netcore.
Written By: Tejas Pitkar
Tejas Pitkar
Tejas Pitkar is a Senior Product Evangelist at Netcore Cloud. He likes analyzing data and diving deep to find valuable insights for marketers. He is credited for writing Industry benchmark reports and marketing leaders’ reports. He also likes to give back to the email industry with his volunteer work at the Only Influencers Diversity Committee. An #emailgeek at heart, he likes writing blogs, sharing email knowledge, and making thought-provoking videos on all things email. He enjoys hiking, backpacking, reading books, and drinking his favorite Chai, in his free time.