diff --git a/app/utils.py b/app/utils.py
index 6b9f8312..07a6582b 100644
--- a/app/utils.py
+++ b/app/utils.py
@@ -1,6 +1,7 @@
 import random
 import string
 import urllib.parse
+from typing import Optional
 
 from unidecode import unidecode
 
@@ -65,3 +66,9 @@ def sanitize_email(email_address: str) -> str:
     if email_address:
         return email_address.lower().strip().replace(" ", "").replace("\n", " ")
     return email_address
+
+
+def sanitize_header(header: Optional[str]) -> Optional[str]:
+    if header:
+        return header.strip().replace("\n", " ")
+    return header
diff --git a/email_handler.py b/email_handler.py
index 1892ee57..a885dd09 100644
--- a/email_handler.py
+++ b/email_handler.py
@@ -118,7 +118,7 @@ from app.models import (
     TransactionalEmail,
 )
 from app.pgp_utils import PGPException, sign_data_with_pgpy, sign_data
-from app.utils import sanitize_email
+from app.utils import sanitize_email, sanitize_header
 from init_app import load_pgp_public_keys
 from server import create_app, create_light_app
 
@@ -1516,6 +1516,13 @@ def handle(envelope: Envelope) -> str:
     envelope.rcpt_tos = rcpt_tos
 
     msg = email.message_from_bytes(envelope.original_content)
+
+    # sanitize email headers
+    msg["from"] = sanitize_header(msg["from"])
+    msg["to"] = sanitize_header(msg["to"])
+    msg["cc"] = sanitize_header(msg["cc"])
+    msg["reply-to"] = sanitize_header(msg["reply-to"])
+
     LOG.d(
         "==>> Handle mail_from:%s, rcpt_tos:%s, header_from:%s, header_to:%s, "
         "cc:%s, reply-to:%s, mail_options:%s, rcpt_options:%s",