v1.0.0

UPGRADE WARNING

Upgrading to this version from version 0.0.X to 1.0.0+ will cause existing code to break. Please see the full usage examples for more details.

Major changes

• Removed public static Attachment FromFile(string filePath, string mimeType, Disposition disposition = Disposition.Attachment, bool validateMimeType = true)
• Replace with public static Attachment FromBase64(string base64Content, string filename, string? mimeType = null, Disposition disposition = Disposition.Attachment, string? contentId = null)
• Removed public static Attachment FromFile(string filePath, string mimeType, Disposition disposition = Disposition.Attachment, bool validateMimeType = true)
• Replaced with public static Attachment FromFile(string filePath, Disposition disposition = Disposition.Attachment, string? contentId = null, string? filename = null, string? mimeType = null)

When creating attachments, the library automatically attempts to determine the MIME type. This detection is based on:

• The filename argument when using Attachment.FromFile or Attachment.FromBase64.
• The filePath when using Attachment.from_file.

If the MIME type cannot be determined, an exception will be raised. Mime types can be manually overridden as demonstrated in the section below.

Attachment MIME Type Deduction Behavior

• When creating attachments, the library automatically determines the MIME type based on the file extension.
• If the MIME type cannot be determined, an exception is raised.

// Create an attachment from disk; the MIME type will be "text/csv", and disposition will be "Disposition.Attachment"
Attachment.FromFile("C:/temp/file.csv");

// This will throw an error, as the MIME type is unknown
Attachment.FromFile("C:/temp/file.unknown");

// Create an attachment and specify the type information. The disposition will be "Disposition.Attachment", filename will be unknown.txt, and MIME type "text/plain"
Attachment.FromFile("C:/temp/file.unknown", filename: "unknown.txt");

// Create an attachment and specify the type information. The disposition will be "Disposition.Attachment", filename will be file.unknown, and MIME type "text/plain"
Attachment.FromFile("C:/temp/file.unknown", mimeType: "text/plain");

New Features

Ability to set the HeaderFrom to be different from the sender address.

 var message = new Message("This is a test email", new MailUser("sender@example.com", "Joe Sender"), new MailUser("noreply@example.com", "Some Business System"));

Inline Attachments and Content-IDs

When creating attachments, they are Disposition.Attachment by default. To properly reference a Content-ID (e.g.,
<img src="cid:logo">), you must explicitly set the attachment disposition to Disposition.Inline.
If the attachment type is set to Disposition.Inline, a default unique Content-ID will be generated.

Using a Dynamically Generated Content-ID

var logo = Attachment.FromFile("C:/temp/logo.png", Disposition.Inline);
message.AddContent(new Content($"<b>Test</b><br><img src=\"cid:{logo.ContentId}\">", ContentType.Html));
message.AddAttachment(logo);

Setting a Custom Content-ID

message.AddAttachment(Attachment.FromFile("C:/temp/logo.png", Disposition.Inline, "logo"));
message.AddContent(new Content("<b>Test</b><br><img src=\"cid:logo\">", ContentType.Html));

Known Issues

There is a known issue where empty file content results in a 400 Bad Request error.

{
  "content": "",
  "disposition": "attachment",
  "filename": "empty.txt",
  "id": "1ed38149-70b2-4476-84a1-83e73913d43c",
  "type": "text/plain"
}

🔹 API Response:

Status Code: 400/BadRequest
Reason: attachments[0].content is required
Message ID:
Request ID: fe9a1acf60a20c9d90bed843f6530156
Raw JSON: {"request_id":"fe9a1acf60a20c9d90bed843f6530156","reason":"attachments[0].content is required"}

This issue has been reported to Proofpoint Product Management.

Limitations

• The Proofpoint API currently does not support empty file attachments.
• If an empty file is sent, you will receive a 400 Bad Request error.

Additional Resources

For more information, refer to the official Proofpoint Secure Email Relay API documentation:
API Documentation

Full Changelog: v0.0.5...v1.0.0