Forbid logins on the SMTP-STARTTLS port

Also, introduce the outline of a framework to handle message sending
differently to message receipt.

internal/smtp/session.go

@@ -1,7 +1,7 @@
 package smtp
 
 import (
-	"fmt"
+	"bytes"
 	"io"
 	"io/ioutil"
 	"log"
@@ -9,26 +9,33 @@ import (
 	"ur.gs/crockery/internal/store"
 )
 
+type Handler interface {
+	Name() string
+	Send(from string, to []string, r io.Reader) error
+}
+
 // type Session implements the User interface for emersion/go-smtp
 type Session struct {
-	ID          uint64
-	Account     *store.Account
-	ServiceName string
+	ID      uint64
+	Account *store.Account
+	Handler Handler
 }
 
 func (s *Session) Send(from string, to []string, r io.Reader) error {
+	// FIXME: TODO: don't keep this lot forever, it's for debugging purposes
 	data, err := ioutil.ReadAll(r)
 	if err != nil {
 		return err
 	}
 
-	log.Printf("%s session %d for %s: from=%s, to=%s, r=<<EOF\n%s\nEOF", s.ServiceName, s.ID, s.Account.Username, from, to, string(data))
+	log.Printf("%s session %d for %s: from=%s, to=%s, r=<<EOF\n%s\nEOF", s.Handler.Name(), s.ID, s.Account.Username, from, to, string(data))
 
-	return fmt.Errorf("Not yet implemented")
+	memR := bytes.NewReader(data)
+	return s.Handler.Send(from, to, memR)
 }
 
 func (s *Session) Logout() error {
-	log.Printf("Ending %s session %d for %s", s.ServiceName, s.ID, s.Account.Username)
+	log.Printf("Ending %s session %d for %s", s.Handler.Name(), s.ID, s.Account.Username)
 
 	return nil
 }