diff --git a/usr.sbin/sendmail/Makefile b/usr.sbin/sendmail/Makefile
--- a/usr.sbin/sendmail/Makefile
+++ b/usr.sbin/sendmail/Makefile
@@ -25,6 +25,13 @@
 BINMODE=2555
 .endif
 
+# Add a pkg(8) trigger that automatically restarts sendmail on upgrade.
+# This is required because if /var/spool/mqueue is deleted and recreated,
+# sendmail will stop working until it's restarted.
+FILESGROUPS=	TRIGGERS
+TRIGGERS=	sendmail.ucl
+TRIGGERSDIR=	/usr/share/pkg/triggers
+
 # Define the database format to use for aliases et al.
 DBMDEF=	-DNEWDB
 # If you don't want NIS alias/map support, comment out this line
diff --git a/usr.sbin/sendmail/sendmail.ucl b/usr.sbin/sendmail/sendmail.ucl
new file mode 100644
--- /dev/null
+++ b/usr.sbin/sendmail/sendmail.ucl
@@ -0,0 +1,34 @@
+/*
+ * SPDX-License-Identifier: ISC
+ *
+ * Copyright (c) 2025 Lexi Winter <ivy@FreeBSD.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+path: [
+	"/var/spool/mqueue",
+	"/var/spool/clientmqueue",
+]
+
+trigger: {
+	type: lua
+	sandbox: false
+	script: <<EOD
+	pkg.exec({"/bin/sh", "-c",
+	    "/usr/sbin/service sendmail status >/dev/null 2>&1 && " ..
+	    "echo 'Restarting sendmail(8).' && " ..
+	    "/usr/sbin/service sendmail restart"})
+EOD
+}
+