Added support for multipart/digest

app/src/main/java/javax/mail/internet/InternetHeaders.java

@@ -434,7 +434,7 @@ public class InternetHeaders {
 		    }
 		    prevline = line;
 		}
-		if (first && android.text.TextUtils.isEmpty(line) && is instanceof ByteArrayInputStream) {
+		if (false && first && android.text.TextUtils.isEmpty(line) && is instanceof ByteArrayInputStream) {
 			// RFC1341 section 7.2.1
 			//   Note that the encapsulation boundary must occur at the beginning of a line, i.e., following a CRLF,
 			//   and that that initial CRLF is considered to be part of the encapsulation boundary rather than part of the preceding part.

app/src/main/java/javax/mail/internet/MimeMultipart.java

@@ -873,6 +873,14 @@ public class MimeMultipart extends Multipart {
 			buf.write(inbuf, 0, inSize);
 		    part = createMimeBodyPart(headers, buf.toByteArray());
 		}
+			try {
+				// https://www.rfc-editor.org/rfc/rfc1521.html#section-7.2.4
+				ContentType ct = new ContentType(getContentType());
+				if ("multipart/digest".equalsIgnoreCase(ct.getBaseType()))
+					part.setHeader("Content-Type", "message/rfc822");
+			} catch (Throwable ex) {
+				eu.faircode.email.Log.e(ex);
+			}
 		super.addBodyPart(part);
 	    }
 	} catch (IOException ioex) {