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Topic: How high is the risk that bulk e-mails sent via ConfTool are identified as spam?

Last year we used special software for sending bulk e-mails, often labeled as spam, even though we did not send many.
We have yet to find a solution to this problem.

Can you explain how ConfTool sends out bulk e-mails?
Do you have any statistics for the e-mails that are labeled as spam, and how do you avoid such problems?
What can we do to avoid such problems?


(A German version of this article is available.)
We cannot completely rule out that e-mails sent via ConfTool are classified as spam, as every spam filter uses its own rules, which are not standardized.
We do not keep spam statistics, but we take a number of measures to make the delivery of your e-mails as reliable as possible.

How ConfTool Sends E-Mails

  • Individual messages: Every e-mail, including bulk e-mails, is sent as an individual message to each recipient and not as one message with many CC or BCC adresses.
  • HTML with plain-text version: Whenever an e-mail is sent in HTML format, it always includes an identical plain-text version.
  • Standards-compliant encoding: The encoding of our e-mails strictly complies with the e-mail standards (SMTP and MIME). Many mail servers check this, and malformed e-mails are a common reason for spam classification.
  • No attachments: E-mails are usually sent without attachments. If you need to send files, please see Sending bulk e-mails with (big) attachments.

Sender Authentication

  • Matching sender address: For each event, we provide a sender address whose domain matches the domain of our mail servers.
  • SPF, DKIM and DMARC: If you use this address as the sender ("From") address, your e-mails pass the SPF check, are signed with DKIM and comply with our DMARC policy. Large e-mail providers such as Google and Yahoo require all three for bulk e-mails.

Please note: If you use a sender address of your own domain instead (e.g. of your university or organization), SPF, DKIM and DMARC cannot be applied for this domain on our side. In this case, your e-mails are considerably more likely to be classified as spam or may even be rejected. We therefore recommend using the sender address we provide for your event.

Transport and Reputation

  • Encrypted transport: Our mail servers deliver e-mails encrypted via STARTTLS or SMTP over TLS whenever the receiving server supports it, using valid TLS certificates.
  • Reverse DNS: All our mail servers have matching reverse DNS (PTR) entries, which many receiving servers require.
  • No blacklist entries: Our mail servers are not listed on any DNS-based blacklists (DNSBL). We also test our configuration with external test tools (see the attached images).

Further Information