Summary
Common causes of 'message rejected as spam' errors for ESPs revolve around poor sender reputation, stemming from factors like high spam complaint rates, sending to invalid email addresses, lack of proper email authentication (SPF, DKIM, DMARC), and triggering content-based spam filters like Vade Retro. Several blocklists, including Spamhaus (SBL and ZEN), URIBL, Return Path Reputation Blocklist (Validity), and BarracudaCentral, actively identify and block spam sources. Dynamic IP addresses and invalid PTR records can also contribute to deliverability issues. Maintaining good email hygiene, monitoring sender reputation through tools like Google Postmaster Tools, Microsoft SNDS, MXToolbox, and GlockApps, and adhering to bulk sender guidelines from providers like Google and Microsoft are crucial for preventing blocklisting.
Key findings
- Spamhaus: Listing on Spamhaus (SBL or ZEN) significantly impacts deliverability.
- Authentication: Lack of SPF, DKIM, and DMARC authentication increases the likelihood of being marked as spam.
- List Hygiene: High bounce rates and spam complaints negatively affect sender reputation.
- Reputation Blocklists: Reputation-based blocklists like Return Path (Validity) and BarracudaCentral are common filters.
- Content Filtering: Content and fingerprint-based filters like Vade Retro can trigger rejections.
- DNS Configuration: Improperly configured PTR records contribute to deliverability problems.
- Dynamic IPs: Sending from dynamic IP addresses is often considered suspicious.
- Monitoring Tools: Tools like Google Postmaster Tools and MXToolbox aid in identifying blocklistings and reputation issues.
- URIBL: Domains listed in URIBL (found in spam emails) negatively impact deliverability.
Key considerations
- Sender Reputation: Proactively monitor sender reputation and promptly address any negative trends.
- List Management: Regularly clean email lists to remove invalid addresses and improve engagement.
- Authentication Standards: Implement and maintain proper SPF, DKIM, and DMARC authentication.
- Content Scrutiny: Carefully review email content and links for anything that might trigger content-based filters.
- DNS Configuration: Ensure accurate PTR records that match sending IPs to domains.
- Bulk Sender Guidelines: Adhere to bulk sending guidelines from major email providers (Google, Microsoft).
- False Positives: Use tools to check for and address potential false positives in spam filtering.
What email marketers say
10 marketer opinions
Common reasons for email rejections and blocklisting for ESPs include poor sender reputation stemming from spam complaints, sending to invalid addresses, and failure to properly authenticate emails using SPF, DKIM, and DMARC. Several blocklists, such as Spamhaus, URIBL, and dynamic IP blacklists (like Spamhaus ZEN), actively identify and block sources of spam. Maintaining good email hygiene practices, including regular list cleaning, segmentation, and monitoring sender reputation through tools like Google Postmaster Tools, Microsoft SNDS, MXToolbox and GlockApps, is crucial. Furthermore, ESPs must enforce strict anti-spam policies to prevent their users from engaging in spam activities, which can lead to the entire ESP being blocklisted.
Key opinions
- Spamhaus: Being listed on Spamhaus, either the SBL or ZEN lists, can cause major deliverability issues due to their widespread use.
- Authentication: Failure to implement SPF, DKIM, and DMARC authentication increases the likelihood of being flagged as spam.
- List Hygiene: Sending to invalid email addresses and high spam complaint rates negatively impact sender reputation and increase the chance of blocklisting.
- Monitoring Tools: Tools like Google Postmaster Tools, Microsoft SNDS, MXToolbox and GlockApps can help identify if you're on a blocklist and monitor sender reputation.
- URIBL: URIBL is a common blocklist that lists domains found in spam emails, so ensuring your links are clean is crucial.
- Dynamic IPs: Sending from dynamic IP addresses can be suspicious and lead to blocklisting.
Key considerations
- Sender Reputation: Actively monitor your sender reputation and address any issues promptly to maintain good deliverability.
- List Management: Regularly clean your email list to remove inactive or invalid addresses to reduce bounce rates and improve engagement.
- Anti-Spam Policies: Enforce strict anti-spam policies for your users to prevent the entire ESP from being blocklisted.
- Authentication Protocols: Implement and maintain proper email authentication using SPF, DKIM, and DMARC to verify your identity and improve deliverability.
- False Positives: Check for false positives with tools and services like Vade Secure sender tool.
Marketer view
Email marketer from Email on Acid recommends monitoring your sender reputation using tools like Google Postmaster Tools and Microsoft SNDS. These tools provide insights into your IP and domain reputation and can help you identify and address deliverability issues.
11 Oct 2022 - Email on Acid
Marketer view
Email marketer from Email Marketing Forum mentions URIBL (Uniform Resource Identifier Block List) as a common blocklist. They explain that URIBL lists domains found in spam emails, so ensuring your links are clean is crucial.
26 Jul 2023 - Email Marketing Forum
What the experts say
5 expert opinions
Common reasons for email rejections and 'message rejected as spam' errors include being listed on reputation-based blocklists like the Return Path Reputation Blocklist (Validity) and having a low SenderBase (Cisco Talos) reputation. Additionally, content or fingerprint-based spam filters, such as Vade Retro, may trigger rejections. Ensuring proper DNS configuration, particularly valid PTR records matching sending IPs to domains, is crucial for avoiding blocklisting.
Key opinions
- Vade Retro: Multiple ISPs might use Vade Retro, a content/fingerprint based spam filter which could be the cause of rejections.
- Content Filtering: Rejection messages suggesting content or fingerprint-based filtering indicate the need to examine links, sending IPs, and click/open trackers for suspicious activity.
- Return Path Blocklist: The Return Path Reputation Blocklist (now Validity) is a widely used blocklist that can cause significant deliverability problems.
- PTR Records: Invalid or missing PTR records are a common cause of deliverability issues and potential blocklisting.
- SenderBase Reputation: A low SenderBase (Cisco Talos) reputation can negatively impact deliverability and lead to message rejections.
Key considerations
- Content Scrutiny: Thoroughly review email content, links, and tracking mechanisms for any elements that might trigger content-based spam filters.
- DNS Configuration: Ensure that PTR records are correctly configured and match sending IP addresses to the corresponding domain.
- Reputation Monitoring: Monitor sender reputation using services like Cisco Talos to identify and address any negative trends promptly.
- Blocklist Checks: Regularly check your IP addresses and domains against common blocklists, including the Return Path Reputation Blocklist, to proactively address any listings.
Expert view
Expert from Word to the Wise shares that SenderBase (now part of Cisco Talos) provides reputation scoring based on email traffic and other factors. A low SenderBase reputation can impact deliverability and potentially lead to message rejections.
25 Nov 2023 - Word to the Wise
Expert view
Expert from Email Geeks suggests that multiple ISPs may be using Vade Retro.
22 Apr 2023 - Email Geeks
What the documentation says
5 technical articles
Common blocklists and services causing 'message rejected as spam' errors include Spamhaus Block List (SBL), Proofpoint's reputation system, BarracudaCentral's reputation blocklist, and the reputation systems of major email providers like Microsoft (Outlook.com) and Google (Gmail). These systems analyze IP addresses, message content, sending behavior, spam complaint rates, bounce rates, user engagement, and adherence to authentication standards (SPF, DKIM, DMARC) and bulk sending guidelines. Listing on these blocklists or failing to meet the requirements of these reputation systems can lead to email rejections or messages being sent to the junk folder.
Key findings
- Spamhaus SBL: The Spamhaus Block List (SBL) is a real-time database of IPs involved in spam, causing email rejections upon listing.
- Proofpoint Reputation: Proofpoint uses a dynamic reputation system based on message content, sending behavior, and IP reputation.
- BarracudaCentral: BarracudaCentral's blocklist relies on real-time network analysis, with listings resulting from poor sending practices, spam, or compromised accounts.
- Outlook.com Reputation: Outlook.com uses a complex system considering spam complaints, bounce rates, and user engagement.
- Gmail Bulk Sender: Google requires SPF, DKIM, DMARC, low spam rates, and easy unsubscribe options for bulk senders; non-compliance causes deliverability problems.
Key considerations
- Monitor Blocklists: Actively monitor blocklist status on services like Spamhaus, Proofpoint, and BarracudaCentral.
- Comply with Guidelines: Adhere to bulk sending guidelines and authentication requirements from Google and Microsoft.
- Improve Reputation: Focus on reducing spam complaints, lowering bounce rates, and increasing positive user engagement (e.g., opens, clicks).
- Analyze Sending Practices: Evaluate sending practices for potential issues like sending spam content or from compromised accounts.
Technical article
Documentation from Google details their bulk sender guidelines, which include authenticating email with SPF, DKIM, and DMARC; keeping spam rates low; and providing easy unsubscribe options. Failure to comply can lead to deliverability issues.
10 Jul 2023 - Google
Technical article
Documentation from Proofpoint explains that they use a reputation system to analyze email traffic and identify spam sources. Their blocklists are dynamic and based on various factors, including message content, sending behavior, and IP reputation.
9 Jul 2023 - Proofpoint
Besides Spamhaus, what blocklists are important for email marketers to monitor?
Does being on a blocklist affect Gmail deliverability?
How can I get delisted from Spamhaus?
How do I check Spamhaus for my IP address and understand the listings?
How do I deal with a SORBS listing affecting email deliverability?
How do I determine the severity and mitigate different email blocklists?
