Display message even when there is no To field.

frontend/src/views/webmail/EmailView.vue

@@ -105,7 +105,7 @@
         <v-spacer />
         <span class="text-grey">{{ email.date }}</span>
       </div>
-      <div class="mt-2 text-grey">
+      <div v-if="email.to.length" class="mt-2 text-grey">
         {{ $gettext('To') }}
         <v-menu v-for="(rcpt, index) in email.to" :key="`to-${index}`">
           <template #activator="{ props }">

modoboa/webmail/lib/imapemail.py

@@ -45,6 +45,7 @@ class ImapEmail(Email):
         self.imapc = self.imapc.__enter__()
         self.mbox, self.mailid = self.mailid.split(":")
         self.attachments: dict[str, str] = {}
+        self.To = []
 
     def __del__(self):
         self.imapc.__exit__()
@@ -69,7 +70,9 @@ class ImapEmail(Email):
         addressbook = self.request.user.addressbook_set.first()
         if not addressbook:
             return
-        contacts = [self.From] + self.To
+        contacts = [self.From]
+        if hasattr(self, "To"):
+            contacts += self.To
         if hasattr(self, "Cc"):
             contacts += self.Cc
         for contact in contacts: