diff --git a/server/apiv1/send.go b/server/apiv1/send.go
index 55ec874..7f006cc 100644
--- a/server/apiv1/send.go
+++ b/server/apiv1/send.go
@@ -80,23 +80,33 @@ type SendRequest struct {
 	Subject string
 
 	// Message body (text)
-	// example: This is the text body
+	// example: Mailpit is awesome!
 	Text string
 
 	// Message body (HTML)
-	// example: <p style="font-family: arial">Mailpit is <b>awesome</b>!</p>
+	// example: <div style="text-align:center"><p style="font-family: arial; font-size: 24px;">Mailpit is <b>awesome</b>!</p><p><img src="cid:mailpit-logo" /></p></div>
 	HTML string
 
 	// Attachments
 	Attachments []struct {
 		// Base64-encoded string of the file content
 		// required: true
-		// example: VGhpcyBpcyBhIHBsYWluIHRleHQgYXR0YWNobWVudA==
+		// example: 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
 		Content string
 		// Filename
 		// required: true
-		// example: AttachedFile.txt
+		// example: mailpit.png
 		Filename string
+		// Optional Content Type for the the attachment.
+		// If this field is not set (or empty) then the content type is automatically detected.
+		// required: false
+		// example: image/png
+		ContentType string
+		// Optional Content-ID (`cid`) for attachment.
+		// If this field is set then the file is attached inline.
+		// required: false
+		// example: mailpit-logo
+		ContentID string
 	}
 
 	// Mailpit tags
@@ -269,9 +279,15 @@ func (d SendRequest) Send(remoteAddr string) (string, error) {
 			if err != nil {
 				return "", fmt.Errorf("error decoding base64 attachment \"%s\": %s", a.Filename, err.Error())
 			}
-
-			mimeType := http.DetectContentType(b)
-			msg = msg.AddAttachment(b, mimeType, a.Filename)
+			contentType := http.DetectContentType(b)
+			if a.ContentType != "" {
+				contentType = a.ContentType
+			}
+			if a.ContentID != "" {
+				msg = msg.AddInline(b, contentType, a.Filename, a.ContentID)
+			} else {
+				msg = msg.AddAttachment(b, contentType, a.Filename)
+			}
 		}
 	}
 
diff --git a/server/server_test.go b/server/server_test.go
index da9a53e..199d969 100644
--- a/server/server_test.go
+++ b/server/server_test.go
@@ -243,6 +243,12 @@ func TestAPIv1Send(t *testing.T) {
 		  {
 			"Content": "VGhpcyBpcyBhIHBsYWluIHRleHQgYXR0YWNobWVudA==",
 			"Filename": "Attached File.txt"
+		  },
+		  {
+			"Content": "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",
+			"Filename": "logo.png",
+			"ContentID": "inline-cid",
+			"ContentType": "overridden/type"
 		  }
 		],
 		"ReplyTo": [
@@ -294,6 +300,10 @@ func TestAPIv1Send(t *testing.T) {
 	assertEqual(t, `Tag 1,Tag 2`, strings.Join(msg.Tags, ","), "wrong Tags")
 	assertEqual(t, 1, len(msg.Attachments), "wrong Attachment count")
 	assertEqual(t, `Attached File.txt`, msg.Attachments[0].FileName, "wrong Attachment name")
+	assertEqual(t, `text/plain`, msg.Attachments[0].ContentType, "wrong Content-Type")
+	assertEqual(t, 1, len(msg.Inline), "wrong inline Attachment count")
+	assertEqual(t, `logo.png`, msg.Inline[0].FileName, "wrong Attachment name")
+	assertEqual(t, `overridden/type`, msg.Inline[0].ContentType, "wrong Content-Type")
 
 	attachmentBytes, err := clientGet(ts.URL + "/api/v1/message/" + resp.ID + "/part/" + msg.Attachments[0].PartID)
 	if err != nil {
diff --git a/server/ui/api/v1/swagger.json b/server/ui/api/v1/swagger.json
index d8444c3..d74983a 100644
--- a/server/ui/api/v1/swagger.json
+++ b/server/ui/api/v1/swagger.json
@@ -1634,12 +1634,22 @@
               "Content": {
                 "description": "Base64-encoded string of the file content",
                 "type": "string",
-                "example": "VGhpcyBpcyBhIHBsYWluIHRleHQgYXR0YWNobWVudA=="
+                "example": "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"
+              },
+              "ContentID": {
+                "description": "Optional Content-ID (`cid`) for attachment.\nIf this field is set then the file is attached inline.",
+                "type": "string",
+                "example": "mailpit-logo"
+              },
+              "ContentType": {
+                "description": "Optional Content Type for the the attachment.\nIf this field is not set (or empty) then the content type is automatically detected.",
+                "type": "string",
+                "example": "image/png"
               },
               "Filename": {
                 "description": "Filename",
                 "type": "string",
-                "example": "AttachedFile.txt"
+                "example": "mailpit.png"
               }
             }
           }
@@ -1698,7 +1708,7 @@
         "HTML": {
           "description": "Message body (HTML)",
           "type": "string",
-          "example": "\u003cp style=\"font-family: arial\"\u003eMailpit is \u003cb\u003eawesome\u003c/b\u003e!\u003c/p\u003e"
+          "example": "\u003cdiv style=\"text-align:center\"\u003e\u003cp style=\"font-family: arial; font-size: 24px;\"\u003eMailpit is \u003cb\u003eawesome\u003c/b\u003e!\u003c/p\u003e\u003cp\u003e\u003cimg src=\"cid:mailpit-logo\" /\u003e\u003c/p\u003e\u003c/div\u003e"
         },
         "Headers": {
           "description": "Optional headers in {\"key\":\"value\"} format",
@@ -1751,7 +1761,7 @@
         "Text": {
           "description": "Message body (text)",
           "type": "string",
-          "example": "This is the text body"
+          "example": "Mailpit is awesome!"
         },
         "To": {
           "description": "\"To\" recipients",