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.deTo 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 attempted transmission
Please note that telephone support is not possible due to the technical complexity.