Group Email Manager

login signup

Investigating and solving email delivery problems for email lists

There are many reasons why an email might not be delivered to a recipient. When a failure occurs, it is normal for a “bounce” to be generated. This bounce normally describes the reason of the failure. The failure may be a permanent problem with the email address (such as it not existing or the account having been closed), or it may be a temporary problem such as a network failure or the content being incorrectly classified as junk.

Bounces generally fall into 2 categories: hard and soft bounces.

  • A hard bounce is a permanent failure and the email delivery will not be retried. A hard bounce is shown as “bounced” in the email delivery page in a Simplelists account.
  • A soft bounce is a temporary failure and delivery will be retried repeatedly until it is either successfully delivered or until it permanently fails after a period of time. A soft bounce is shown as “deferred” in the email delivery page in a Simplelists account.

This page provides details of the most common bounces and some information to assist with solving them.

For any of the problems detailed below, it is always possible to retrieve specific delivery details from your Simplelists dashboard, within the “email delivery” menu. The delivery details will show the exact error from the recipient server (if applicable) or will show the delivery receipt information for successful deliveries. This information can be provided to a recipient for them to pass to their email administrator and will help them investigate and locate the problem.

The following headings show the various error messages that may be shown for failed email deliveries.

Content of email is blocked

This problem is generally caused by something in the content of the email that the receiving email server does not like. It could be a particular keyword that has triggered a spam filter at the server, or it could be a particular attachment of type of attachment that is banned. Sometimes it is the general tone of the email that triggers a spam filter.

This error tends to be intermittent for certain recipients. Some emails will be rejected (maybe only very occasionally) and most will probably be delivered successfully.

To solve this problem it is best for the recipient in question to contact their email provider with the details of the failed delivery.

Recipient has blocked the message

This error generally happens when a recipient or their email administrator has blocked something specific about the list email. It may be the specific sender of the email or something more general.

To solve this problem it is necessary for the recipient or their email administrator to lift the restriction in question.

Server has rejected the message

This error happens when something on the recipient’s email system has blocked the email. This could be a policy block based on the sending IP address of the server or it could be something more general.

To solve this problem it is necessary for the recipient or their email administrator to lift the restriction in question.

Server has blocked the message as suspected spoofing

This error happens when the receiving server suspects that the email being delivered is spoofed. This happens when an email system receives an email externally which looks like one that should only be generated internally. This is to protect against phishing attacks whereby an employee is impersonated by an outside attacker. For Simplelists, the error can occur when someone in a company sends an email to a Simplelists list which is then delivered back to the same server to recipients who are part of the same company. For example, bob@widgets.com might send an email to a Simplelists list which then gets delivered to jane@widgets.com.

There are a number of technical solutions to mitigate the problem of spoofing such as DKIM and DMARC, so this problem is not as widespread as it might seem it could be. Nonetheless, there are some systems (notably Mimecast) which automatically reject such emails.

There are a number of ways to solve this problem:

  • Ask the sender’s email administrator to whitelist Simplelists’ IP addresses
  • Ask the sender’s email administrator to consider implementing a DMARC of reject or quarantine
  • Change a list’s settings in Simplelists to not modify list emails. This can be done by removing any settings that may change the email’s content such as list footers, headers and subject prefixes. This will ensure that an email’s DKIM signature is not broken which will reduce (but not remove) the risk of spoofing rejections.
  • Change a list to always send from the list email address instead of the original sender’s email address. This has the disadvantage that it can be more difficult to see who the email was originally sent by but it will reduce the risk of spoofing errors.

    • Envelope sender of email rejected

    This error means that the server blocked the email address of the envelope sender (this is not necessarily the same as the sender of the email). For Simplelists, this will normally be the email address of the list.

    To solve this problem it is necessary for the recipient or their email administrator to lift the restriction in question.

    Suspected email loop

    The email is with in an infinite mail loop or has passed through so many servers that the recipient server suspects it is in a mail loop.

    To solve this problem further investigation will be needed by either Simplelists support staff or by the administrator of the receiving email server.

    Message too large for recipient

    The email being delivered was too large for the recipient’s mailbox to accept. This may be because the size on its own was above the maximum accepted by the receiving email server, or it may be that the size of the email would push the recipient over their mailbox limit.

    To solve this problem either the recipient will need to arrange for their mailbox limit to be increased, or the email should be resent with smaller attachments.

    Recipient mailbox is full

    The recipient’s mailbox is full and is not accepting emails.

    To solve this problem the recipient will need to clear space in their mailbox.

    Recipient’s mailbox is not ccepting email

    The recipient’s mailbox is not accepting emails. The exact cause of this is unknown, but for some reason the recipient’s mailbox is not accepting emails. It may be that the mailbox has been disabled or locked, or it may be that the email address has no account associated with it.

    To solve this problem it is necessary for the recipient to raise a support call with their email administrator.

    Receiving email server is rate-limiting email receipt

    The receiving email server is rate-limiting inbound connections. This is caused by the receiving email server either being overloaded or restricting the rate of emails being received for some other reason. It may be that the account in question is receiving emails from many sources at a rate that is too high (possibly because of an attack) or it may be that Simplelists is sending emails too quickly. In the case of the latter, Simplelists will normally back-off and retry at a slower rate.

    To solve this problem it is normally necessary for the administrator of the receiving email server to investigate and find out the cause of them rate-limiting. Sometimes no action is needed and this problem will sort itself.

    Network error

    This error is caused by some sort of connection problem between Simplelists and the receiving email server. Sometimes this is caused by a network problem somewhere between the 2 servers; sometimes it is caused by errors at the receiving server which result in lost connectivity.

    Sometimes this problem will solve itself and Simplelists will retry the emails. At other times it may be necessary for Simplelists to route emails through a different server in order to workaround any intermediate network connectivity issues.

    Blocked attachments

    The email has been rejected because it contained file attachments that are blocked. These may be the specific content of the attachments, or it may be the type of file extension of the attachment.

    To solve this problem the email should be resent without attachments or with the attacments in a different format.

    Blocked format of email

    The email has been blocked due to its format. This is likely because of its failure to fully comply with internet email standards that dictate how emails should be sent or because of a failure of SPF or DKIM.

    To solve this problem it may be necessary to send the email from a different email client. It should also be checked that the DNS settings for the Simplelists account are correct, for SPF and DKIM records. These can be viewed in the “domains” tab of “general settings”.

    Sender of email is blocked

    The sender of the email has been blocked either by the recipient or by the recipient’s email system.

    To solve this problem it will be necessary to contact the recipient or their email adminsitrator to find out more details of the blocked sender.

    Policy rejection at the recipient

    A policy at the receiving email server has resulted in this email being rejected. The policy could have been something about the email being sent such as its content or sending server, or it could be a more general policy rejecting emails for the recipient.

    To solve this problem it will be necessary to contact the recipient or the recipient’s email administrator.

    Email blocked at the network level

    The email has been blocked due to network-related rules. This may be because the sending IP address of the Simplelists’ server has been blocked by the recipient’s email server, or it may be a more general network issue which is causing connections to be blocked. It is also possible that the recipient is forwarding their emails to another email address and that it is the forwarding system whose IP address is blocked (i.e. the emails are being successfully delivered by Simplelists to the recipient’s listed server, and then that server is forwarding the emails elsewhere).

    To solve this problem it will be neccessary to contact the recipient or the recipient’s email administrator to find out why the connections are being blocked. It may be necessary to whitelist Simplelists IP addresses, the list of which can be obtained from Simplelists support.

    Unknown recipient

    The recipient email address has been rejected as unknown by the receiving email server. This is normally due to an email address being entered incorrectly or the email address no longer existing (for example the recipient may have moved elsewhere).

    To solve this problem check that the email address has been entered correctly, and contact the recipient by other means to check their email address.

    Unknown domain

    The domain of the email address cannot be found. This normally happens because of an email address being mistyped. It can also happen if the domain cannot be contacted from the region the email is being sent from.

    To solve this problem check that the domain of the email address has been entered correctly. If it is definitely correct, contact Simplelists support to see if emails should be rerouted via a different region.

    Email address has changed

    The recipient’s email address has changed and this email address is no longer valid.

    Firstly check the detailed bounce message to see if the new email address is stated. Failing that, contact the recipient by other means to find out their new email address.

    Invalid email address

    The email address is invalid. This is normally caused by an email address being mistyped. Unlike the “unknown recipient” error, this could be an invalid email address format which never existed.

    To solve this problem, check the email address and try again.

    Access denied

    This is a very generic error, often generated by Microsoft. Quite often it means that the email address was previously valid but now no longer exists. It may be that the recipient has moved elsewhere and their account has now been disabled. It can also be caused by policy restrictions at the receiving system.

    To solve this problem first check that the email address is still valid. If it is, the recipient should contact their email administrator to find out why the emails are being rejected.

    SPF or DKIM failure

    The email has been rejected due to a failure of SPF, DKIM or DMARC authentication standards. For Simplelists, this will normally be because the DNS records of an account have not been or are no longer set up correctly.

    To solve this problem, check the DNS settings of your account in the “domains” tab of “general settings”.

    Relaying denied

    Relaying emails for the recipient has been denied at the receiving server. This is likely caused by a misconfiguration at the recipient’s email system.

    To solve this problem it will be necessary to contact the recipient or the recipient’s email administrator.

    Server error

    This is a fairly general error that has been caused by some sort of issue at the recipient’s email server. Viewing the bounce message in the “email failures” page of the “email delivery” menu may sshow additional specific information.

    To solve this problem it will be necessary to contact the recipient or the recipient’s email administrator.

    Authentication required

    The receiving email server has reported that authentication is required in order for it to take receipt of this email.

    To solve this problem it will be necessary to contact the recipient or the recipient’s email administrator.

    Email address only available for internal use

    The receiving email server does not accept email from external sources for this email address.

    To solve this problem it will be necessary to contact the recipient or the recipient’s email administrator.

    Unknown error

    The actual cause of the email delivery failure is not known. Further information may be available by viewing the bounce message in the “email failures” page of the “email delivery” menu of your Simplelists dashboard.

    To solve this problem Simplelists support may be able to provide additional information, or it may be necessary to contact the recipient or the recipient’s email administrator.

    Open relay

    The receiving email server has identified the sending email server as an open relay and has therefore blocked the email. It is unlikely that Simplelists is the cause of the open relay, so it may be that the email has transgressed through another server that is an open relay.

    To solve this problem it will be necessary to contact the recipient or the recipient’s email administrator.

    Email unrouteable

    The email address in question is unrouteable and therefore cannot be delivered.

    To solve this problem it will be necessary to contact the recipient or the recipient’s email administrator.

    Date of the email is too far in the past or future

    The date of the email is considered too far in the past or the future for the receiving email system and the email has therefore been rejected.

    This can sometimes happen when old emails that were help for moderation are approved. To solve this, ensure that any such emails are moderated more promptly.

    The region that the email is sent from is blocked

    The location of the sending server is blocked by the recipient server. This may be Simplelists’ server or it may be an intermediate server.

    In order to rectify this, Simplelists can route emails via different regions. Contact Support to find out more details.

    Attachments have stripped from email

    This is a notification that attachments contained in the original email have been stripped. It is not a bounce message and should not have been sent as a bounce message.

    Contact the recipient and notify them that messages regarding attachments being stripped are being incorrectly sent as bounces.

    Receipient is rate-limiting emails

    The recipient’s email account is limiting the rate at which emails are being received and this email has been rejected. This can sometimes happen when an account is the subject of an attack with many emails being sent to it.

    There is little that can be done to resolve this, other than waiting or contacting the recipient by other means.

    Automated reply

    This bounce is an automated reply rather than necessarily a delivery error.

    Review the automated reply by viewing the bounce, and check whether there is any information such as a change in email address. Notify the recipient that there automated replies are being sent as bounces rather than to the original sender of the email.

    Problems further downstream when delivering the email

    Errors have been returned further downstream after Simplelists has delivered the email to the first destination.

    This error has happened outside of the control of Simplelists at a provider after the recipient’s first email server. Contact the recipient by other means to notify them of the problem.