diff --git a/conservancy/usethesource/models.py b/conservancy/usethesource/models.py
index 84afcf204a42e08127ef57e80f3ff937230fe7f9..70b05b0cae7da8b197c6b120698865185d6d8acf 100644
--- a/conservancy/usethesource/models.py
+++ b/conservancy/usethesource/models.py
@@ -4,6 +4,11 @@ from django.contrib.auth.models import User
 from django.db import models
 
 
+def gen_message_id():
+    """Generate a time-based identifier for use in "In-Reply-To" header."""
+    return f'<{uuid.uuid1()}@sfconservancy.org>'
+
+
 class Candidate(models.Model):
     """A source/binary release we'd like to verify CCS status of."""
 
@@ -16,6 +21,7 @@ class Candidate(models.Model):
     source_url = models.URLField()
     binary_url = models.URLField(blank=True)
     ordering = models.SmallIntegerField(default=0)
+    email_message_id = models.CharField(max_length=255, default=gen_message_id)
 
     class Meta:
         ordering = ['ordering', 'name']
@@ -24,11 +30,6 @@ 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."""
 
@@ -48,14 +49,14 @@ class Comment(models.Model):
             return None
 
     def in_reply_to(self):
-        """Determine the message_id of the previous comment.
+        """Determine the message_id of the previous comment or the candidate.
 
         Used for email threading.
         """
         if prev_comment := self._find_previous_comment():
             return prev_comment.email_message_id
         else:
-            return None
+            return self.candidate.email_message_id
 
     class Meta:
         ordering = ['id']