Use 8bit transfer encoding for the text body if SMTP server advertises 8BITMIME. In all other cases base64 is still used (including saved copies in IMAP "Sent" folder).

Feel free to revert this if anything breaks.

src/com/fsck/k9/mail/Message.java

@@ -143,4 +143,6 @@ public abstract class Message implements Part, Body
     }
 
     public abstract void saveChanges() throws MessagingException;
+
+    public abstract void setEncoding(String encoding);
 }

src/com/fsck/k9/mail/Multipart.java

@@ -3,6 +3,9 @@ package com.fsck.k9.mail;
 
 import java.util.ArrayList;
 
+import com.fsck.k9.mail.internet.MimeHeader;
+import com.fsck.k9.mail.internet.TextBody;
+
 public abstract class Multipart implements Body
 {
     protected Part mParent;
@@ -55,4 +58,25 @@ public abstract class Multipart implements Body
     {
         this.mParent = parent;
     }
+
+	public void setEncoding(String encoding)
+	{
+		for (BodyPart part : mParts)
+		{
+			try
+			{
+				Body body = part.getBody();
+				if (body instanceof TextBody)
+				{
+					part.setHeader(MimeHeader.HEADER_CONTENT_TRANSFER_ENCODING, encoding);
+					((TextBody)body).setEncoding(encoding);
+				}
+			}
+			catch (MessagingException e)
+			{
+				// Ignore
+			}
+		}
+		
+	}
 }

src/com/fsck/k9/mail/internet/MimeMessage.java

@@ -369,9 +369,9 @@ public class MimeMessage extends Message
     {
         this.mBody = body;
         setHeader("MIME-Version", "1.0");
-        if (body instanceof com.fsck.k9.mail.Multipart)
+        if (body instanceof Multipart)
         {
-            com.fsck.k9.mail.Multipart multipart = ((com.fsck.k9.mail.Multipart)body);
+            Multipart multipart = ((Multipart)body);
             multipart.setParent(this);
             setHeader(MimeHeader.HEADER_CONTENT_TYPE, multipart.getContentType());
         }
@@ -431,6 +431,19 @@ public class MimeMessage extends Message
         return null;
     }
 
+    public void setEncoding(String encoding)
+    {
+    	if (mBody instanceof Multipart)
+    	{
+    		((Multipart)mBody).setEncoding(encoding);
+    	}
+    	else if (mBody instanceof TextBody)
+        {
+            setHeader(MimeHeader.HEADER_CONTENT_TRANSFER_ENCODING, encoding);
+            ((TextBody)mBody).setEncoding(encoding);
+        }
+    }
+
     class MimeMessageBuilder implements ContentHandler
     {
         private Stack stack = new Stack();

src/com/fsck/k9/mail/internet/TextBody.java

@@ -9,7 +9,8 @@ import java.io.*;
 
 public class TextBody implements Body
 {
-    String mBody;
+    private String mBody;
+    private String mEncoding;
 
     public TextBody(String body)
     {
@@ -21,9 +22,16 @@ public class TextBody implements Body
         if (mBody != null)
         {
             byte[] bytes = mBody.getBytes("UTF-8");
+            if ("8bit".equals(mEncoding))
+            {
+                out.write(bytes);
+            }
+            else
+            {
                 out.write(Base64.encodeBase64Chunked(bytes));
             }
         }
+    }
 
     /**
      * Get the text of the body in it's unencoded format.
@@ -57,4 +65,9 @@ public class TextBody implements Body
             return null;
         }
     }
+
+    public void setEncoding(String encoding)
+    {
+    	mEncoding = encoding;
+    }
 }

src/com/fsck/k9/mail/transport/SmtpTransport.java

@@ -57,6 +57,7 @@ public class SmtpTransport extends Transport
     PeekableInputStream mIn;
 
     OutputStream mOut;
+    private boolean m8bitEncodingAllowed;
 
     /**
      * smtp://user:password@server:port CONNECTION_SECURITY_NONE
@@ -184,6 +185,8 @@ public class SmtpTransport extends Transport
 
             List<String> results = executeSimpleCommand("EHLO " + localHost);
 
+            m8bitEncodingAllowed = results.contains("8BITMIME");
+
             /*
              * TODO may need to add code to fall back to HELO I switched it from
              * using HELO on non STARTTLS connections because of AOL's mail
@@ -285,10 +288,19 @@ public class SmtpTransport extends Transport
     {
         close();
         open();
+
+        if (m8bitEncodingAllowed)
+        {
+            //TODO: Make sure that we don't have lines that are longer than
+            // 998 bytes (don't count characters!)
+            message.setEncoding("8bit");
+        }
+
         Address[] from = message.getFrom();
         boolean possibleSend = false;
         try
         {
+        	//TODO: Add BODY=8BITMIME parameter if appropriate?
             executeSimpleCommand("MAIL FROM: " + "<" + from[0].getAddress() + ">");
             for (Address address : message.getRecipients(RecipientType.TO))
             {
@@ -304,9 +316,13 @@ public class SmtpTransport extends Transport
             }
             message.setRecipients(RecipientType.BCC, null);
             executeSimpleCommand("DATA");
+            
+            //TODO: Data stuffing (RFC 821 4.5.2.)
             EOLConvertingOutputStream msgOut = new EOLConvertingOutputStream(
                     new BufferedOutputStream(mOut, 1024)); 
+
             message.writeTo(msgOut);
+
             // We use BufferedOutputStream. So make sure to call flush() !
             msgOut.flush();