diff --git a/conservancy/usethesource/models.py b/conservancy/usethesource/models.py
index 08d0969956727fdbecd72aba253727eb4d980a1c..84afcf204a42e08127ef57e80f3ff937230fe7f9 100644
--- a/conservancy/usethesource/models.py
+++ b/conservancy/usethesource/models.py
@@ -1,14 +1,18 @@
+import uuid
+
 from django.contrib.auth.models import User
 from django.db import models
 
 
 class Candidate(models.Model):
+    """A source/binary release we'd like to verify CCS status of."""
+
     name = models.CharField('Candidate name', max_length=50)
     slug = models.SlugField(max_length=50, unique=True)
     vendor = models.CharField('Vendor name', max_length=50)
     device = models.CharField('Device name', max_length=50)
-    release_date = models.DateField()
-    description = models.TextField()
+    release_date = models.DateField(null=True, blank=True)
+    description = models.TextField(blank=True)
     source_url = models.URLField()
     binary_url = models.URLField(blank=True)
     ordering = models.SmallIntegerField(default=0)
@@ -20,14 +24,38 @@ class Candidate(models.Model):
         return self.name
 
 
+def gen_message_id():
+    """Generate a time-based identifier for use in "In-Reply-To" header."""
+    return f'<{uuid.uuid1()}@sfconservancy.org>'
+
+
 class Comment(models.Model):
+    """A comment about experiences or learnings building the candidate."""
+
     candidate = models.ForeignKey(Candidate, on_delete=models.CASCADE)
     user = models.ForeignKey(User, on_delete=models.PROTECT)
     time = models.DateTimeField(auto_now_add=True)
     message = models.TextField()
+    email_message_id = models.CharField(max_length=255, default=gen_message_id)
 
     def __str__(self):
-        return f'{self.candidate.name}, {self.user}, {self.time}'
+        return f'{self.id}: {self.candidate.name}, {self.user}, {self.time}'
+
+    def _find_previous_comment(self):
+        try:
+            return self.__class__.objects.filter(candidate=self.candidate, id__lt=self.id).latest('id')
+        except self.__class__.DoesNotExist:
+            return None
+
+    def in_reply_to(self):
+        """Determine the message_id of the previous comment.
+
+        Used for email threading.
+        """
+        if prev_comment := self._find_previous_comment():
+            return prev_comment.email_message_id
+        else:
+            return None
 
     class Meta:
         ordering = ['id']