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Are you aware of email bounces? What is it? When a server rejects an email, it is called an email bounce. The most common reasons behind email bounces are permanent or temporary issues with the email account your sending to receiving emails or the email is blocked by the receiving server.

When there is an email bounce, the recipient’s server sends back a message to the senders email. Typically by reading the message it sends back to you, you will be able to indicate the issue immediately.

Here are 10 reasons the email you sent was bounced back to you.

1. Mailbox Full

One of the reasons for email bounces can be the inbox of the recipient is full. There are numerous email applications that have a defined storage capacity for every individual to use for email. for instance 2GB of space for all emails received and sent from their email box. Keep in mind this includes documents and photos. If this limit exceeds, the server won’t allow any more emails as well as usually alert the mailbox owner so that an action can be taken to resolve the issue.

2. Message Too Large

Sometimes the content in the message or attachment is too large and exceeds the limit of the receiving server. The headers, text, and images larger than the actual allowed size of the recipient’s mailbox make the content in the message too lengthy. It is recommended to send messages smaller. Anything over 10MG is too large in most cases.

3. DNS Failure

In the case of DNS failure, the email can’t be delivered as there is an issue with the receiving server’s DNS. The issue can be with the nameserver settings for your domain so it’s better to contact your domain administrator for help. Note that the issue may be due to the SPF records too. This issue may or may not be termed as temporary. Also, the DNS failure error might occur, if the mail server is down or a typo error occurred when it was set up or the destination domain isn’t available.

4. Vacation/ Auto Reply

If someone goes on vacation or can’t check their email, your emails to them will bounce. It’s important to note that, unlike with other bounce categories, this type of bounce means your email was successfully delivered to the inbox.

Carefully monitor how often this email address ends up in this category. If months go by and the person hasn’t returned from vacation, you may want to consider removing the contact.

5. Blacklisted

When an email server of the recipient is blocking inbound mail from the sender’s server due to blacklisting, it is termed as general mail blocking. A mail block is recorded when the receiver’s server blocks an email completely, ultimately rejecting the message with attempting to deliver it to the inbox.

The most common reasons for this block are:

  • The address with which you reply is blacklisted.

  • One of the IPs through which mail is sent is temporarily blocked.

  • One of the domains through which mail is sent is temporarily blacklisted.

  • The server that receives emails only accepts white-listed senders.

6. Known Spammer

Your recipient’s email server might be marking emails sent from your account depending on an email history or reputation which indicates you have been sending spam emails.

The most common reasons for this bounce are as below:

  • The email sent by you over time to the mail server has been constantly appearing as spam and so it has stopped delivering email to its users from you.

  • One of the IPs through which mail is sent is temporarily blocked

  • One of the domains through which mail is sent is temporarily blacklisted.

  • Reply-to address or brand name has a poor reputation.

7. Undeliverable E-mail

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.

8. The Email Has Been Blocked by the Recipient

Individuals can block emails from senders they no longer want to hear from. If that has happened to you, a bounce will be generated.

9. Attachment Detected

If there’s an attachment in the message, the recipient’s email server might block your mail. The attachment might have been identified as a possible virus source or the system won’t be allowing attachments at all or specific types of files might have been blocked by the system (e.g. .exe).

Additionally, the size of the attachment might also cause an issue. Note that your attachment size doesn’t exceed 10MB.

10. You Typed the Wrong E-mail Address

In this type of bounce, the recipient mail server is unable to deliver your email because the address was spelled incorrectly. The bounce back message will indicate the email address you typed does not exist.


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