diff --git a/CHANGELOG.md b/CHANGELOG.md
index c50806f5..4dd9438a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -122,6 +122,7 @@ v1.6.0 - 2019-01-18
 - Bug: Fetched accounts: Password field is of type "text" ([#789](https://github.com/Mailu/Mailu/issues/789))
 - Bug: Auto-forward destination not accepting top level domains ([#818](https://github.com/Mailu/Mailu/issues/818))
 - Bug: DOMAIN_REGISTRATION=False in .env was not treated correctly ([#830](https://github.com/Mailu/Mailu/issues/830))
+- Bug: Internal error when checking null sender address ([#846](https://github.com/Mailu/Mailu/issues/846))
 
 v1.5.1 - 2017-11-21
 -------------------
diff --git a/core/admin/mailu/internal/views/postfix.py b/core/admin/mailu/internal/views/postfix.py
index e94bfc28..0b229825 100644
--- a/core/admin/mailu/internal/views/postfix.py
+++ b/core/admin/mailu/internal/views/postfix.py
@@ -49,5 +49,18 @@ def postfix_sender_login(sender):
 def postfix_sender_access(sender):
     """ Simply reject any sender that pretends to be from a local domain
     """
-    localpart, domain_name = models.Email.resolve_domain(sender)
-    return flask.jsonify("REJECT") if models.Domain.query.get(domain_name) else flask.abort(404)
+    if not is_void_address(sender):
+        localpart, domain_name = models.Email.resolve_domain(sender)
+        return flask.jsonify("REJECT") if models.Domain.query.get(domain_name) else flask.abort(404)
+    else:
+        return flask.abort(404)
+
+
+def is_void_address(email):
+    '''True if the email is void (null) email address.
+    '''
+    if email.startswith('<') and email.endswith('>'):
+        email = email[1:-1]
+    # Some MTAs use things like '<MAILER-DAEMON>' instead of '<>'; so let's
+    # consider void any such thing.
+    return '@' not in email