Email error messages

To ensure the security of our systems and a high delivery rate for all users, our spam filter checks outgoing messages for certain characteristics. If your email was blocked, this is often due to technical details that could jeopardize the reputation of our mail server.

How to optimize your email for smooth delivery:

• Subject line: Use a meaningful subject. Avoid leaving it empty or starting/ending it with special characters such as ? or !.

• Recipient fields: Always enter at least one primary recipient in the “To” field. Pure BCC mailings often look suspicious to filters.

• Links & URLs: Link transparently. Do not use URL shorteners and make sure the displayed link text matches the actual destination.

• Technical cleanliness: Ensure correct header values (From, Reply-To, etc.) according to common email standards (RFC). Outdated email programs or misconfigurations in the client can cause issues here.

• List hygiene: Process bounces promptly and remove invalid addresses from your distribution lists.

• Troubleshooting tip: Check the source code of your email (in webmail via right-click -> “View source”), to identify technical inconsistencies directly.

Please understand that for security reasons we cannot provide detailed insights into our filter logic in order to keep protection against spam consistently high.

To ensure your emails arrive reliably, a clean recipient list is crucial. If our system detects that messages cannot be delivered repeatedly, a protective mechanism is triggered.

What happened?

At least one of the recipient addresses you use no longer exists or the recipient’s mailbox is permanently blocked. To protect the reputation of your access (and our mail servers), our system has temporarily paused delivery to these specific addresses.

We recommend the following steps:

• Check details: You will receive a separate notification from us (bounce mail). It lists the affected email addresses exactly.

• Clean up your address list: Please remove these addresses from your distribution list or correct any possible typos.

Why is this important?

Continuous failed attempts to invalid addresses can cause major providers (such as Gmail or Outlook) to generally classify your emails as spam. By applying the temporary block, we protect your delivery rate.

Our system temporarily stops accepting emails when, within a very small time window, an unusually high number of messages with similar characteristics is detected. This is an important security measure against automated spam and phishing attempts.

What you can do now:

• Short pause: Please wait a few minutes before starting the sending process again. In most cases, the block regulates itself after a short waiting period.

• Check sending volume: If you are sending a newsletter or bulk/serial emails, ideally spread the sending over a longer period.

• Review content: Make sure your email does not show typical spam indicators.

To ensure the security of our systems and a high delivery rate for all users, our spam filter checks outgoing messages for certain characteristics. If your email was blocked, this is often due to technical details that could endanger the reputation of our mail server.

Possible reasons for the block:

• Suspicious sending behavior: Recently, an unusually high number of messages were sent from your address and were classified as spam.

• Content: Your emails contain characteristics that are very similar to past spam/phishing emails.

What you can do now:

• Check the content: Make sure your email does not show typical spam characteristics. For example, this can include deceptive URLs in the text or misleading sender names.

Please understand that, for security reasons, we cannot provide detailed insights into our filtering logic in order to keep protection against spam consistently high.

To ensure the security of our systems and a high delivery rate for all users, our spam filter checks outgoing messages for certain characteristics. If your email was blocked, this is often due to technical details that could harm the reputation of our mail server.

Possible reasons for the block:

• Suspicious sending behavior: In the past few days, an unusually high number of messages were sent from your address and classified as spam.

• Content: Your emails contain characteristics that closely resemble past spam/phishing emails.

How to optimize your email for smooth delivery:

• Subject line: Use a meaningful subject. Avoid leaving it blank or starting/ending it with special characters like ? or !.

• Recipient fields: Always enter at least one primary recipient in the “To” field. Pure BCC mailings often appear suspicious to filters.

• Links & URLs: Link transparently. Do not use URL shorteners and make sure the displayed link text matches the actual destination.

• Technical cleanliness: Ensure correct header values (From, Reply-To, etc.) according to common email standards (RFC). Outdated email programs or misconfigurations in the client can cause issues here.

• List hygiene: Process bounces promptly and remove invalid addresses from your distribution lists.

Please understand that, for security reasons, we cannot provide detailed insights into our filter logic in order to keep protection against spam consistently high.

To ensure the security of our systems and a high delivery rate for all users, our spam filter checks outgoing messages for certain characteristics. If your email was blocked, this is often due to technical details that could jeopardize the reputation of our mail server.

Possible reasons for the block:

• Suspicious sending behavior: From your address, an unusually high number of messages were sent recently and were classified as spam.

• Content: Your emails have characteristics that are very similar to past spam/phishing emails.

How to optimize your email for smooth delivery:

• Subject line: Use a meaningful subject. Avoid leaving it empty or starting/ending it with special characters like ? or !.

• Recipient fields: Always enter at least one primary recipient in the “To” field. Pure BCC mailings often look suspicious to filters.

• Links & URLs: Link transparently. Do not use URL shorteners and make sure the displayed link text matches the actual destination.

• Technical cleanliness: Ensure correct header values (From, Reply-To, etc.) according to common email standards (RFC). Outdated email programs or misconfigurations in the client can cause issues here.

• List hygiene: Process bounces immediately and remove invalid addresses from your distribution lists.

Please understand that for security reasons we cannot provide detailed insights into our filter logic in order to keep protection against spam consistently high.

Our system has blocked email sending from your current IP address. This is done automatically to prevent misuse of our infrastructure.

Possible reasons for an IP block:

• Suspicious sending behavior: Recently, an unusually high number of messages were sent from your IP address and were classified as spam.

• Security risk on end devices: Sometimes computers or smartphones send messages in the background without you noticing (e.g., via malware), which can lead to an automatic block.

• Shared IP addresses: If you use a public or shared IP address, the activity of other users in the same network may have triggered the block.

We recommend the following steps:

• Run a virus scan: For your safety, check your devices for malware to ensure that there is no unauthorized access.

• Restart the router: Often, simply unplugging your internet router briefly helps. This usually allows you to receive a new IP address from your internet provider.

• Contact support: If the issue persists, our team is happy to help. We will review the case individually and can lift the block manually if needed.

Background: This measure not only protects our mail servers from ending up on blocklists worldwide, but also secures your account against misuse by third parties.

To ensure that system emails are delivered reliably, they should only be sent to valid recipients. If our system detects that messages cannot be delivered repeatedly, a protective mechanism is triggered.

What happened?

At least one of the recipient email addresses you use for emails triggered by cron jobs no longer exists, or the recipient’s mailbox is permanently locked. To protect the reputation of your account (and our mail servers), our system has temporarily paused sending to these specific addresses.

We recommend the following steps:

• Check details: You will receive a separate notification from us (bounce email). It lists the affected email addresses exactly.

• Check cron jobs: Please remove these email addresses from the settings of your cron jobs in KAS or correct any typos.

Why is this important?

Repeated failed attempts to invalid email addresses can cause major providers (such as Gmail or Outlook) to generally classify your emails as spam. With the temporary block, we protect your delivery rate.

Your email could not be delivered because the message was sent via a server that is currently on our internal blacklist.

Why did this happen?

This block usually does not affect you personally or your specific email address, but the network of your email provider (e.g., Microsoft Office 365 / Outlook). If certain IP ranges from the provider send large volumes of spam or phishing emails, we must temporarily block these ranges to protect our own customers and systems.

What can you do now?

Since the cause is in your email provider’s network, we have no direct influence on resolving the block. We recommend forwarding the error message to their technical support. They must ensure that abusive sending via their servers is stopped.

Your email could not be delivered because the sending server or its IP you use currently has an unusual or negative reputation. Our system has therefore temporarily throttled reception from this server.

Why is delivery limited?

This measure automatically takes effect when a specific IP address generates a high volume of unwanted emails (spam) within a short time. To protect our users from a flood of spam emails, we only allow a strongly limited number of emails from such servers within a given time window. Throttling also gives legitimate senders another chance for delivery, while spam sending is effectively slowed down.

What can you do now?

The cause of the rating lies with the sending server. A manual removal of the throttling is not possible.

• Patience: Since this is a temporary throttling, the mail is often delivered with a delay once the sending volume from this IP drops again.

• Inform your provider: Contact your email provider and send the error message, including the mentioned IP address.

• Check reputation: Your provider must ensure that no spam is sent via its IP addresses and that they are not listed on public blacklists.

Email delivery has been delayed because your email fails the DMARC security check.

What exactly happens here?

Instead of immediately and permanently rejecting the email, our server asks the sending mail server to resend the message after a short waiting time (about 15 minutes).

Why do we do this?

• Spam filtering: Real, reputable mail servers try delivery again automatically after a short time. Basic spam scripts usually stop after the first failed attempt.

• Chance to fix it: We give the sending system the opportunity to verify the delivery. If the email fails the DMARC check again on the next attempt, it may be permanently rejected (Rejected) to protect the recipient.

What does this mean for you?

The message is delayed on the first attempt with the note “Greylisted due to DMARC policy failure”. You do not need to take action, as your mail server will automatically try to deliver the email again. If the email is finally rejected on the next delivery attempt, you should correct your DMARC and SPF/DKIM settings.

Our systems aborted the delivery attempt because the email got stuck in an endless loop. This means the message is repeatedly sent back and forth between different mail servers or mailboxes, without ever reaching its destination for good.

How does such a loop occur?

A mail loop is usually caused by conflicting settings. Common causes include:

• Circular forwarding: Mailbox A forwards to mailbox B, and mailbox B (directly or via detours) forwards back to mailbox A.

• Automatic replies: A (misconfigured) autoresponder (e.g., an out-of-office notice) replies to another automatic email, triggering an endless chain of replies.

• Faulty aliases: Multiple email addresses are linked in a way that sends the message in circles.

What can you do now?

Because such a loop jeopardizes the mail server’s function, sending is automatically stopped. Please check the following points:

1. Check forwarding: Verify whether you or the recipient have set up forwards that could lead in circles.

2. Autoresponder: Check whether automatic replies (out-of-office notices) are active on both sides at the same time.

Background: Without this protective mechanism, the mail servers involved would try to deliver the message millions of times, which could cause the systems to crash or completely overwhelm the mailboxes.