● Covered by 1 source · 1 reportLow impact1 negative
Email clients should not use multipart/alternative for error messages
Key points
- Multipart/alternative is for interchangeable content, not error messages.
- Sending "Plain text version not available" is unhelpful and confusing.
- Users preferring plain text may miss actual email content.
- Email clients should handle rendering errors, not the sender.
Misuse of Multipart/Alternative
The author argues against using the multipart/alternative MIME type to deliver error messages like "Plain text version not available." This standard is intended for presenting the same information in multiple interchangeable formats, typically an HTML version alongside a plain text counterpart. Using it for error messages deviates from its defined purpose.
Recipient Experience
When an email client is configured to prefer plain text or cannot render HTML, receiving an email with "Plain text version not available" as the plain text part is unhelpful. The user is presented with a non-informative message, even when the HTML part contains the actual email content. This can lead to confusion and a missed message, as the user might not realize the full content is recoverable.
Scenarios of Impact
The issue affects users with older email clients, MIME-capable clients unable to handle HTML, and those who configure their clients to prefer plain text. In all these scenarios, the error message provides no actionable information and can obscure the actual email content. The author suggests that if no plain text part were included, the client's default error handling might be more effective or offer better recovery options.
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Primary sources
GitHub apache/spamassassinReporting from
An email user criticizes the practice of sending "Plain text version not available" as the plain text part of a multipart/alternative email, arguing it misuses the standard and provides no value to recipients. This practice can confuse users whose email clients prefer plain text or cannot render HTML, potentially hiding the actual email content.