diff --git a/UPDATING b/UPDATING
index 2ffd1baaf472..14fae1eb0656 100644
--- a/UPDATING
+++ b/UPDATING
@@ -27,6 +27,13 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 15.x IS SLOW:
 	world, or to merely disable the most expensive debugging functionality
 	at runtime, run "ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20240201:
+	sendmail 8.18.1 has been imported and merged.  This version enforces
+	stricter RFC compliance by default, especially with respect to line
+	endings.  This may cause issues with receiving messages from
+	non-compliant MTAs; please see the first 8.18.1 release note in
+	contrib/sendmail/RELEASE_NOTES for mitigations.
+
 20240111:
 	Commit cc760de2183f changed the internal interface between
 	the nfscommon and nfscl modules.  As such, both need to be