Are there mails which cannot be forwarded

Yes, there are several types of emails that cannot be forwarded:

  1. Emails with specific headers: Some emails have specific headers that prevent forwarding. For example, emails with the "X-MS-Exchange-Organization-AuthResult" header are typically not forwardable.
  2. Emails with authentication headers: Emails that use authentication headers, such as SPF (Sender Policy Framework) or DKIM (DomainKeys Identified Mail), may not be forwardable. These headers are used to verify the authenticity of the email and may not be preserved during forwarding.
  3. Emails with encrypted attachments: Emails with encrypted attachments, such as PGP (Pretty Good Privacy) or S/MIME (Secure/Multipurpose Internet Mail Extensions), may not be forwardable. The encryption key is typically tied to the original sender's email address, making it difficult to forward the email without compromising the encryption.
  4. Emails with proprietary formats: Emails that use proprietary formats, such as Microsoft Outlook's.msg files, may not be forwardable. These formats are specific to the email client or platform and may not be compatible with other email clients or platforms.
  5. Emails with large attachments: Emails with very large attachments may not be forwardable due to size limitations imposed by email servers or email clients. For example, some email clients may have a maximum attachment size of 10MB, while others may have a maximum size of 25MB.
  6. Emails with specific content: Some emails may contain specific content that prevents forwarding, such as:
    • Emails with embedded images or multimedia content that are not compatible with the recipient's email client or platform.
    • Emails with complex formatting, such as HTML tables or CSS styles, that may not be preserved during forwarding.
    • Emails with specific character sets or encoding that may not be supported by the recipient's email client or platform.
  7. Emails with anti-forwarding mechanisms: Some email senders may use anti-forwarding mechanisms, such as email filters or rules, to prevent emails from being forwarded. These mechanisms can detect and block forwarded emails, preventing them from being delivered to the intended recipient.

It's worth noting that while these types of emails may not be forwardable, they may still be able to be copied and pasted into a new email or saved as a file.