Reasons for rejecting an e-mail

This article describes the reasons why an e-mail is rejected by us.

If you have been informed by a sender that it was not possible to deliver an email to you, the sender's email server is configured incorrectly.

The following reasons lead to an immediate rejection of the incoming e-mail:

• RDNS entry from the e-mail server differs or has not been set
• SPF hard fail
• E-mail server is on a real-time blocklist (RBL)
• E-mail ENVELOPE sender is on a real-time blocklist (RBL)
• E-mail FROM domain is on a real-time blocklist (RBL)
• E-mail contains a virus
• DKIM signature is invalid
• DMARC policy setting 'REJECT
• At least one e-mail attachment contains a dangerous executable file
• The recipient's e-mail address does not support e-mail reception (e.g. due to a noreply e-mail address)
• The maximum size of an e-mail has been exceeded (100 MB)
• The e-mail does not comply with RFC 5322 (https://www.rfc-editor.org/rfc/rfc5322)

Real-Time Blocklists (RBL)

If the sender's mail server is listed on a real-time blocklist, the sender receives the following error message in the SMTP dialog:

550 5.7.1 Service unavailable; client [123.123.123.123] blocked using b.barracudacentral.org; from=bounces@newsletter.top-remise.com, to=john-doe@creoline.de

To ensure future delivery, the sender's mail server must be removed from the real-time blocklist. The following RBLs are used to check incoming emails:

zen.spamhaus.org

The sender's mail server can be removed from the real-time blocklist via the Spamhaus Blocklist Removal Center.

mail.abusix.zone

The sender's mail server can be removed from the real-time blocklist using the Delist function.

mail.bl.blocklist.de

The sender's mail server can be removed from the real-time blocklist using the Delist function.

psbl.surriel.com

The sender's mail server can be removed from the real-time blocklist using the Removal Form.

spam.spamrats.com

The sender's mail server can be removed from the real-time blocklist using the Removal Form.

dyna.spamrats.com

The sender's mail server can be removed from the real-time blocklist using the Removal Form.

noptr.spamrats.com

The sender's mail server can be removed from the real-time blocklist using the Removal Form.

b.barracudacentral.org

The sender's mail server can be removed from the real-time blocklist via a Removal Request.

cbl.abuseat.org

The sender's mail server can be removed from the real-time blocklist via a Removal Request.

block.ascams.com

The sender's mail server can be removed from the real-time blocklist via a Removal Request.

recent.spam.dnsbl.sorbs.net

The sender's mail server can be removed from the real-time blocklist via a Removal Request.

dnsbl.cobion.com

The sender's mail server can be removed from the real-time blocklist via a Removal Request.

Dangerous executable content

The following file types cannot be sent as attachments:

• application/javascript (js,jsm,mjs)
• application/x-executable
• application/x-java (class)
• application/x-ms-dos-executable (exe)
• message/partial
• Files with the extension: VBS
• Files with the extension: PIF
• Files with the extension: INK
• Files with the extension: EXE
• Files with the extension: SHS
• Files with the extension: SHB
• Files with the extension: JAR
• Files with the extension: BIN
• Files with the extension: ISO

Support

If, despite checking all the above factors, an e-mail is still rejected, we will be happy to provide you with detailed clarification.

Please send us an email to support@creoline.com to let us know which specific email was rejected. We need the following information to be able to process your request:

• Sender e-mail address
• Recipient e-mail address
• Date and time of the sending attempt
• Exact error message including log ID

Example error message and log ID:

554 5.7.1 This message was blocked because its content presents a potential security issue.
Please visit https://creol.ink/qek6x to review our message content and attachment content guidelines.
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