Knowledgebase

Email bounces can be very frustrating for business communication and marketing. As bad and discomforting as email bounces could be, it is still considered a normal outcome of every email marketing campaign and something to be expected. But what is more important is that when they occur, you should understand how to troubleshoot and get them resolved.

Also read: How to Fix Email Deliverability Problems

What are Email Bounces

It simply means the email you sent failed to deliver. This happens whether you are sending from webmail or using a third party email clients such as Outlook. In most cases, you will receive a notification on the failure and the details will spell out the reason for the bounce.

In this post, we are concerned about the several things that could be causing email bounces and how they can be resolved.

Three main types of email bounces

There are two types of email bounces — a soft bounce and a hard bounce.

1. Soft Bounce

A soft bounce means that the email address is valid and was delivered to the recipient’s inbox, but it still bounced because the mailbox was full, the server was down, or the message was too large for the recipient’s inbox.

2. Hard Bounce

A hard bounce happens when the email is permanently rejected because the email address is invalid or the email address doesn’t exist.

Now that you understand the two basic types of email bounces, let’s take a look at the common reasons why emails might bounce.

3. General bounce

A general bounce describes a situation where the email bounces because the recipient doesn’t receive the email due to the technical limitations of the server. The cause is here, not so specifically stated or defined but linked to some technical limitations like receiver’s firewall settings restricting your emails. This type of email bounce is safe and doesn’t affect email account and sender reputation.

Also read:  Basic Steps to Improve Your Email Delivery

Causes of Email Bounces

Lets explore in greater detail the specific causes of email bounce and how to address them.

• Maximum emails per hour has been exceeded. This can be caused by forwarders or by mailing lists. The default is 150 per hour. Feel free to contact us via phone or live chat if you would like this increased. Please include detailed information regarding why you need the limit increased.
• Disk quota reached. This can be caused if one of the accounts has reached or exceeded its Disk Quota for the email account. This can, at times, cause other email addresses on the account to not be able to send email. There will also be problems when sending an email from an online external email client such as Hotmail, Yahoo, or Gmail to that email address. The email will bounce back as undeliverable.
• Blocked email. If the email addresses are placed within the “Blocked” category, the receiving server has blocked the incoming email. This is often the case among government institutions or schools, where servers can be more strict when it comes to receiving emails. To resolve this issue, you need to get in touch with the contact and request that their system administrators unblock the IP addresses.
• email server down. Exim, the local MTA (mail transfer agent), could be down on the server.
• Backed up email queues. Our mail proxy servers could have their email queues backed up. When this happens, please be patient as there will be a delay of 3-4 hours before the email is delivered.
• Mistyped email address. Sometimes, an email address is mistyped causing a bounce back. This is easy to correct as the bounced back email header will tell you that the email you have attempted to send your mail to does not exist. When you receive such notification, you will simply need to check the email address and make the necessary corrections.

• Receiving Server Blacklist. Similar to the above problem and as explained with the sending server blacklist, you will also be unable to send emails to a server that has been blacklisted for spamming. The server will not be able to receive your mails and you will get a bounce back notification.

• Sending Server Blacklist. You will not be able to send emails from a server that had been blacklisted for spamming. You will also not be able to receive emails into accounts hosted on a server that has been blacklisted for spamming. The good news is that most servers will hold emails and attempt to resend them for up to 72 hours. Within that period, any issues is expected to have been resolved.

• Non-Existent Emails. You receive bounce back emails sometimes because the mail had been sent an email account that does not exist. This occurs under certain conditions::

  1. The domain name to which the email was directed has expired and has not been renewed. As a result the domain DNS could have been redirected to another server address or deleted. In such cases, all emails created with that domain name ceases to function.
  2. The mail belonged to an employee who has left the organization and so his email has been deleted.
  3. The email has been inactive or unused for a long time and deleted by the email server for inactivity.

• Undeliverable email. If bounced emails are in the “Undeliverable” category, that means that the receiving email server is temporarily unavailable, was overloaded, or couldn’t be found. A server that can’t be found could have crashed or been under maintenance, so this may just mean waiting to send the email to the address again. However, if this email address repeatedly bounces on multiple emails, it may mean the server is gone for good.

• Email size is too large: This simply means that the email file size is larger than the allowable file size allowed on the recipient server. Email size is an important factor for email bounce back. This could be caused by large attachments. In other cases, some email service providers allow only text emails and so when images are attached, it could cause a bounce. In this case, sending emails with rich text and images makes your email bounce back.

Also read: How to Troubleshoot and Resolve Email Problems

How to Fix Email Bounce Back Issues

There are simple way to address email bounce back issues especially from the point of a normal email user.

1. Understand The Reason For The Bounce.

The first step is to understand why the bounce occurred. You can easily do this by carefully going through the bounced back email to uncover the reason for the bounce. Usually, the bounced message will tell you why your email could not be delivered. If it says the email address does not exist, for instance, you need to verify the address to be sure it is typed correctly, check to verify that the domain name is still active or if there is a temporary server failure.

2. Take Steps to Fix Issues

Once you have identified why your email could not be delivered, the next thing you do is to take appropriate steps to address the issues. This could include entering your email address correctly, waiting for recipient server issues to be addressed before trying again or addressing issues with sender server such as getting server IP out of a blacklist.

3. Send emails consistently

Sending emails consistently to an email address can tell the server that your email is one to trust and not just a spammy sender. When there is a constant flow of messages between two accounts, the receiver server gets an assurance of the quality of the email conversation which makes your account less vulnerable to email bounces.

4. Avoid Free Sender Domains

Free email accounts like @gmail.com, @outlook.com and @yahoo.com does not allow you to authenticate your email account making them targets of spam filters and increasing the likelihood of bounces. The solution to this is to send your emails from your registered domain name rather than a free service.

5. Contact Your Web Host

In difficult circumstances where your efforts to fix the issues are not yielding the desired results, it is most appropriate to contact your web host to fix things up. Usually, your web host should the expertise to address these issues or have an internal company mechanism to address them. So, you can always rely on your web host when it seems difficult for you to handle your email bounce back issues.

6. Improve Your Sender Reputation Score

The sender’s reputation score measures the health of our email program. It is graded between 0 and 100 to identify the quality of your sender reputation and how mailbox providers view your IP address. A low sender reputation simply tells you that you are likely to have more bounces, more email messages going into the spam folder or getting an outright block.

There are many free tools that can help you assess our email sender reputation. One is Sender Score.

7. Maintain Time Frame Between Consecutive Emails

The time gap between your emails can matter a lot because email service provider’s algorithms believe that no human can send multiple emails at one go. You may not have made mistakes in typing your destination email address or made any other errors but the gap between your emails may suggest a machine-automated operation and that can cause a bounce. So when the time gap between your emails does not look natural and possible with human senders, you could get a block and bounces. It is ideal to think that a human sender can send a short message within 90 seconds. The longer the time gap, the better and safer.

How Do Servers Get Blacklisted Causing Email Bounce Back Issues?

Server protection against spam is essential not just for the users but also for the integrity of the server and entire network. Spam is a huge problem on the Internet and as a mail server operator it is important to take reasonable steps to ensure that the server is secured from being hijacked by those wishing to distribute bulk unsolicited e-mails.

The first thing is to ensure that the server is properly configured to secure it against spam attacks. If the server is not configured correctly, spammers can use the mail server to dispatch messages through the server uninhibited. Mail servers accept messages for recipients that have their mailboxes hosted on the mail server itself, but it is critical to regulate who can send messages to others (non-local recipients). Secure the server by configuring strict rules as to who can use the server to send messages (relay messages) to non-local recipients.

Carefully review any domain redirections mail users may have set up on the server. If mail users have been permitted to redirect their mail to other mail systems then they will also be redirecting any spam to those mail systems. These mail systems will detect the server as spamming and this may cause the server to be blacklisted as a result. As such, in a hosted environment, either moderate the use of redirections, or prevent users from redirecting their mailboxes by disabling the feature in web mail entirely.

It is possible to get blacklisted or have your server IP(s) blacklisted via notifications being incorrectly sent to a forged senders address. Here are the common ways that notifications or bounced messages where replies to a forged address from a message envelope can have you added to a blacklist;

If a message is sent an address on the server that is associated with a list and the sender is not validated as an authenticated sender, a notification is sent to the original sender which may be forged, hence sending messages to an invalid account.

If an action on a filter is set up to "notify sender" that the message has met a particular criteria of a filter and the senders address is forged, then the message sent from the server could be again notifying the original forged senders address.

Having quotas set up on the mailboxes on a server will send out notifications to senders where a mailbox has exceeded its quota limit. This sent reply could be to a forged email sender which after a period of time can result in blacklisting.

The reply message from a disabled mailbox or domain could be sending its rejection messages to a forged sender address.

Another way that your server could be blacklisted is through blacklisting of a range by a DNSBL. Here is a returned warning from the web site of a DNSBL after a server range has been blacklisted. DNSBL means Domain Name System Blacklists, also known or DNS Blacklists. These are spam blocking lists that allow a website administrator to block messages from specific systems that have a history of sending spam. As their name implies, the lists are based on the Internet's Domain Name System, which converts complicated, numerical IP address such as 140.239.191.10 into domain names like example.net, making the lists much easier to read, use, and search. If the maintainer of a DNS Blacklist has in the past received spam of any kind from a specific domain name, that server would be "blacklisted" and all messages sent from it would be either flagged or rejected from all sites that use that specific list.

If the server is not secured from unauthorized relay, it will end up on an Open Relay Blacklist. Once the server is on a black list, the removal process is very time consuming.

How to remove a server from a blacklist

First, check the status of your website to understand its true reputation. Check Here

The removal process is as follows:

1. First ensure that your server is no longer open relay. Make sure that the server is configured properly and protected from any exploitation.

2. Next, determine which open relay black lists the server is listed on..

3. Finally, go to the web sites of each Blacklist provider and use their web site to submit your site for testing. The process would vary. You will have to follow the processes if you want to be removed from any blacklists because databases often share IP addresses that have been listed. Once you've fixed things on your end, go back to the blacklist's site and follow their instructions for the IP address removal process. Here's what you're likely to come across:

Self-Service Removal. There are a few blacklists with a self-service removal feature that lets you take your IP address off the list without much trouble. However, you'll want to make sure you've resolved any issues before doing this. If you don't and your IP address gets listed again, it won't be easy to get it removed that next time.

Time-Based Removal. Most blacklists have a built-in, automatic process that removes lower-level listings (IP addresses that are light offenders) within a week or two. But if the IP address had sent spam more than once or did a high volume, the time period will be longer.

4. Blacklist providers usually process removal requests within 24 hours. They will send a mail message to indicate the status of the removal.

In addition, you can do the following:

Scan all computers on your network for viruses

See if there are any known and needed "patches" (updates and fixes) for your operating system

Configure routers more securely

Establish and enforce stronger passwords

Check your server logs for any possible exploitation which could be related to outdated software.

Final Words

It does not matter who your web host is or the strength and credibility of your email platform, bounces will always occur and it is not out of place to have an email bounce back. When they do, it is important to try and have them resolved. In this tutorial we will examine the circumstances that lead to bounce back and how to get them resolved when they do occur.