diff --git a/addons/mail/static/src/less/thread.less b/addons/mail/static/src/less/thread.less
index 22d51a17863..81ab0f917d0 100644
--- a/addons/mail/static/src/less/thread.less
+++ b/addons/mail/static/src/less/thread.less
@@ -129,6 +129,9 @@
                 display: inline-block;
                 word-break: break-all;
             }
+            img {
+                max-width: 100%;
+            }
 
             .o_mail_body_long {
                 display: none;