Summary
ISPs reject emails at the RCPT TO command and send abuse reports due to a combination of factors related to sender reputation, list hygiene, authentication, and spam prevention. These rejections often happen before the email body is transferred, indicating a preliminary check failure. Key reasons include poor sender reputation (high complaint rates, blacklist listings, spam trap hits), inadequate list hygiene (sending to invalid or inactive addresses), missing or misconfigured email authentication records (SPF, DKIM, DMARC), and spam-like content or sender behavior. Additionally, greylisting and specific policies like SPFBL can cause temporary or permanent rejections. Abuse reports generated through feedback loops also contribute, as ISPs may reject future emails if the sender doesn't address the issues. Essentially, these rejections signify that the sending server is deemed untrustworthy or is engaging in practices that are indicative of spam.
Key findings
- Sender Reputation: Poor sender reputation (high complaints, blacklist listings, spam traps) is a primary driver of rejections.
- List Hygiene: Poor list hygiene (invalid addresses, spam traps) increases bounce rates, complaints, and the likelihood of rejection.
- Email Authentication: Missing or misconfigured SPF, DKIM, and DMARC records lead ISPs to flag emails as suspicious and reject them.
- Blacklists: Being listed on public or private blacklists results in immediate rejection during the SMTP transaction.
- Abuse Reports: Abuse reports generated through feedback loops (FBLs) contribute to rejection if underlying issues are not addressed.
- Greylisting: Greylisting leads to temporary rejections as a spam-filtering technique.
- Local Policy: ISPs can reject based on their local policies and spam filtering criteria.
Key considerations
- Monitor Sender Reputation: Regularly monitor sender reputation and promptly address any issues affecting it.
- Practice List Hygiene: Maintain clean email lists by removing invalid addresses, spam traps, and unengaged subscribers.
- Implement Email Authentication: Configure SPF, DKIM, and DMARC records correctly to authenticate emails and prevent spoofing.
- Address Abuse Reports: Participate in feedback loops (FBLs) and promptly address any abuse reports received.
- Avoid Spam Triggers: Avoid using spam-like language and ensure emails comply with anti-spam regulations (e.g., CAN-SPAM).
- Monitor Engagement: Track email engagement metrics (opens, clicks) and remove unengaged subscribers from your list.
What email marketers say
11 marketer opinions
ISPs reject emails at the RCPT TO command and send abuse reports due to various factors related to sender reputation, list hygiene, authentication, and spam prevention. Rejection at this stage often occurs before the email body is fully transferred, indicating a preliminary check failure. Key reasons include poor sender reputation stemming from spam complaints, hitting spam traps, being listed on blacklists, and lack of engagement. Inadequate list hygiene practices, such as sending to invalid or inactive addresses, also contribute to rejections. Moreover, missing or misconfigured email authentication records (SPF, DKIM, DMARC) can flag emails as suspicious. Temporary rejections may also occur due to greylisting. Addressing these issues is crucial for improving email deliverability.
Key opinions
- Sender Reputation: Poor sender reputation, influenced by spam complaints, blacklist listings, and low engagement, is a primary cause for rejection.
- Spam Traps: Hitting spam traps indicates poor list hygiene and can immediately damage sender reputation, leading to rejections.
- Blacklists: Being listed on real-time blacklists (RBLs) results in immediate rejection by ISPs.
- List Hygiene: Poor list hygiene, including sending to invalid or inactive email addresses, increases bounce rates and spam complaints, leading to rejections.
- Authentication: Missing or misconfigured SPF, DKIM, and DMARC records can flag emails as suspicious and cause rejections.
- Engagement: Low engagement rates (opens, clicks) signal that the sender is not sending relevant emails, potentially leading to rejections and spam filtering.
- Greylisting: Greylisting can cause temporary rejections at the RCPT TO stage as a spam-filtering technique.
Key considerations
- Monitor Reputation: Regularly monitor sender reputation using tools like Google Postmaster Tools and address any issues promptly.
- Clean Email Lists: Implement robust list hygiene practices, including removing invalid and inactive email addresses, and use double opt-in for subscriptions.
- Implement Authentication: Ensure that SPF, DKIM, and DMARC records are correctly configured to authenticate emails and prevent spoofing.
- Encourage Engagement: Send relevant and engaging content to encourage opens and clicks, improving sender reputation.
- Feedback Loops: Participate in feedback loops to receive and process abuse reports, addressing complaints promptly to prevent future issues.
- Avoid Spam Traps: Implement strategies to avoid hitting spam traps, such as validating email addresses and using reputable list providers.
Marketer view
Email marketer from SendGrid explains that hitting spam traps can immediately damage sender reputation, potentially leading to rejections at the RCPT TO stage.
26 Jan 2022 - SendGrid
Marketer view
Email marketer from NeilPatel.com explains that poor sender reputation, marked by high spam complaints, can cause ISPs to reject emails even before delivery attempts.
4 Mar 2025 - NeilPatel.com
What the experts say
4 expert opinions
ISPs reject emails at the RCPT TO command and generate abuse reports primarily due to poor list hygiene, low sender reputation, feedback loop abuse reports, and blocklist listings. Sending to invalid addresses and spam traps signals poor list management, leading to rejections. Low sender reputation, resulting from high complaint rates and spam trap hits, causes ISPs to reject emails during the SMTP handshake. Abuse reports from feedback loops directly notify senders of spam complaints, and failure to address these issues can result in rejections. Furthermore, being listed on public or private blocklists because of spam-like activity leads to immediate rejections as ISPs consult these lists during the SMTP transaction.
Key opinions
- Poor List Hygiene: Sending emails to invalid addresses and spam traps indicates poor list hygiene and can lead to rejections and abuse reports.
- Low Sender Reputation: Low sender reputation, derived from high complaint rates, blacklist listings, and spam trap hits, prompts ISPs to reject emails.
- Feedback Loop Abuse: Failure to address abuse reports from feedback loops can result in future email rejections.
- Blocklist Listings: Being listed on public or private blocklists due to spam-like activity leads to immediate rejections.
Key considerations
- Maintain List Hygiene: Regularly clean email lists by removing invalid addresses and spam traps to prevent rejections and abuse reports.
- Monitor Sender Reputation: Monitor sender reputation to identify and address issues, such as high complaint rates and blacklist listings.
- Address Abuse Reports: Promptly address abuse reports from feedback loops to prevent future rejections.
- Avoid Spam-Like Activity: Implement best practices to avoid spam-like activity and prevent being listed on blocklists.
Expert view
Expert from SpamResource states that a low sender reputation, derived from high complaint rates, blacklist listings, and spam trap hits, leads ISPs to reject email during the SMTP handshake at RCPT TO.
18 Jun 2022 - SpamResource
Expert view
Expert from SpamResource explains that sending email to invalid addresses or known spam traps results in rejections and abuse reports, as it signals poor list hygiene and potential spamming practices.
30 Dec 2024 - SpamResource
What the documentation says
4 technical articles
ISPs reject emails at the RCPT TO command due to local policy, spam filtering, poor sender reputation, and failed authentication checks. The RCPT command allows servers to reject recipients based on various criteria before accepting the message data. High spam complaint rates negatively affect sender reputation, leading to rejections or spam placement. Emails with spam-like characteristics or from IPs with poor reputation may be rejected at the connection or RCPT TO level. DMARC policies allow domain owners to instruct receiving mail servers to reject emails that fail authentication checks.
Key findings
- Local Policy: Servers can reject recipients based on local policy or other criteria.
- Spam Filtering: ISPs use spam filtering techniques to identify and reject unwanted emails.
- Poor Sender Reputation: High spam complaint rates negatively affect sender reputation, leading to rejections.
- Spam-Like Characteristics: Emails with spam-like characteristics may be rejected.
- Failed Authentication: DMARC policies instruct receiving servers to reject emails that fail authentication checks.
Key considerations
- Monitor Complaints: Monitor spam complaint rates and address any issues to improve sender reputation.
- Implement Authentication: Implement DMARC policies and ensure proper email authentication to prevent rejections.
- Avoid Spam Triggers: Avoid sending emails that exhibit spam-like characteristics.
- Review Local Policies: Understand and adhere to local policies of receiving servers to avoid rejections.
Technical article
Documentation from Google Postmaster Tools explains that high spam complaint rates will negatively affect your sender reputation and lead to emails being rejected or sent to spam.
21 Feb 2023 - Google
Technical article
Documentation from ietf.org defines the RCPT command and explains that servers can reject recipients based on local policy, spam filtering, or other criteria before accepting the message data.
7 Apr 2022 - ietf.org
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