Email delivery errors arise from a combination of technical issues, list hygiene problems, sender reputation concerns, and content-related factors. Technical reasons include SMTP errors (e.g., mailbox unavailable, transaction failed), rate limiting, and bad attachments. List hygiene issues encompass invalid email addresses, spam traps, bounces (hard and soft), and inactive subscribers. Sender reputation is affected by high bounce rates, spam complaints, and blocklisting. Additionally, the use of spam trigger words can negatively impact deliverability. Monitoring error codes, managing bounce rates, and maintaining a clean email list are crucial for optimizing email delivery.
10 marketer opinions
Delivery errors in email marketing stem from a variety of issues, including technical problems like bad attachments, rate limits, and server errors, as well as list hygiene issues such as invalid email addresses, spam traps, and high bounce rates. Sender reputation is a critical factor, influenced by spam complaints and blocklisting. Understanding the difference between hard and soft bounces is important for email list management and deliverability.
Marketer view
Email marketer from Sendinblue shares causes for email bounces include spam traps, invalid email addresses, blocked senders, and server issues. These issues can affect sender reputation. Sendinblue documentation helps identify and resolve these errors, ensuring better deliverability.
24 Sep 2021 - Sendinblue
Marketer view
Email marketer from Reddit user u/EmailExpert mentions that using spam trigger words in subject lines and email content can cause delivery errors. Avoiding these words is important for improving deliverability. User adds it is important to keep your content as clean as possible
8 Mar 2024 - Reddit
2 expert opinions
Delivery errors are significantly influenced by sender reputation and blocklisting. A poor sender reputation, arising from high bounce rates, spam complaints, and blacklisting, results in ISPs blocking or filtering emails. Monitoring and proactively addressing blocklist status is crucial for maintaining email deliverability.
Expert view
Expert from Word to the Wise shares that being on blocklists will definitely cause delivery errors. Regularly monitoring blocklist status helps identify and resolve issues that impact email delivery. Proactive monitoring is key to avoiding deliverability problems.
21 Mar 2023 - Word to the Wise
Expert view
Expert from SpamResource explains that poor sender reputation can lead to delivery errors. Factors like high bounce rates, spam complaints, and blacklisting contribute to a negative reputation, causing ISPs to block or filter emails. Maintaining a good sender reputation is key to successful delivery.
1 Aug 2024 - SpamResource
4 technical articles
Delivery errors are classified using SMTP error codes and bounce types. Common SMTP errors include mailbox unavailable (550), transaction failed (554), and temporary failures (450/451). Bounce types are hard (permanent, invalid address) and soft (temporary, full inbox). Feedback loops, like those in AWS SES, notify senders of spam complaints. RFC 5321 provides detailed SMTP protocol information.
Technical article
Documentation from RFC 5321 details SMTP error codes, including 550 for mailbox unavailable and 421 for service not available. These codes help diagnose delivery issues. RFC 5321 provides a comprehensive overview of SMTP protocol.
18 Apr 2025 - RFC Editor
Technical article
Documentation from AWS SES explains about feedback loops. AWS documentation describes permanent bounces due to non-existent addresses and transient bounces due to temporary issues. AWS SES also uses feedback loops to notify senders of spam complaints.
7 Jan 2023 - AWS SES
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