Discard periods prefixing SMTP data per RFC 821 4.5.2

examples/dotmail

@@ -0,0 +1,14 @@
+To: Blah <blah@blah.com>
+From: Me <me@sj26.com>
+Subject: Whatever
+Content-Type: text/plain
+
+Plain text mail
+
+With some dot lines:
+
+.
+
+...
+
+Done.

lib/mail_catcher/smtp.rb

@@ -34,7 +34,10 @@ class MailCatcher::Smtp < EventMachine::Protocols::SmtpServer
 
   def receive_data_chunk(lines)
     current_message[:source] ||= ""
-    current_message[:source] += lines.join("\n")
+    lines.each do |line|
+      # RFC821 4.5.2 says leading periods should be stripped from the body data.
+      current_message[:source] << line.sub(/\A\./, "") << "\n"
+    end
     true
   end