fix(smtp_server): updated line split logic, normalize all linebreaks to \r\n (#897)

Co-authored-by: Vishnu S <vishnu@zerodha.com>

lib/postal/smtp_server/server.rb

@@ -147,15 +147,16 @@ module Postal
                   # Client went away
                   eof = true
                 end
+
+                # Normalize all \r\n and \n to \r\n
+                buffers[io] = buffers[io].encode(buffers[io].encoding, universal_newline: true).encode(buffers[io].encoding, crlf_newline: true)
+
                 # We line buffer, so look to see if we have received a newline
                 # and keep doing so until all buffered lines have been processed.
-                while buffers[io].index("\n")
+                while buffers[io].index("\r\n")
                   # Extract the line
-                  if buffers[io].index("\r\n")
-                    line, buffers[io] = buffers[io].split("\r\n", 2)
-                  else
-                    line, buffers[io] = buffers[io].split("\n", 2)
-                  end
+                  line, buffers[io] = buffers[io].split("\r\n", 2)
+
                   # Send the received line to the client object for processing
                   result = client.handle(line)
                   # If the client object returned some data, write it back to the client