diff --git a/store/db/mysql/inbox.go b/store/db/mysql/inbox.go
index ad80e0a8..db8df0d5 100644
--- a/store/db/mysql/inbox.go
+++ b/store/db/mysql/inbox.go
@@ -2,6 +2,7 @@ package mysql
 
 import (
 	"context"
+	"database/sql"
 	"strings"
 
 	"github.com/pkg/errors"
@@ -132,3 +133,13 @@ func (d *DB) DeleteInbox(ctx context.Context, delete *store.DeleteInbox) error {
 	}
 	return nil
 }
+
+func vacuumInbox(ctx context.Context, tx *sql.Tx) error {
+	stmt := "DELETE FROM `inbox` WHERE `sender_id` NOT IN (SELECT `id` FROM `user`)"
+	_, err := tx.ExecContext(ctx, stmt)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
diff --git a/store/db/mysql/mysql.go b/store/db/mysql/mysql.go
index 2c8da727..6f478e2f 100644
--- a/store/db/mysql/mysql.go
+++ b/store/db/mysql/mysql.go
@@ -72,6 +72,9 @@ func (d *DB) Vacuum(ctx context.Context) error {
 	if err := vacuumMemoRelations(ctx, tx); err != nil {
 		return err
 	}
+	if err := vacuumInbox(ctx, tx); err != nil {
+		return err
+	}
 	if err := vacuumTag(ctx, tx); err != nil {
 		// Prevent revive warning.
 		return err
diff --git a/store/db/postgres/inbox.go b/store/db/postgres/inbox.go
index 1191e414..66460d34 100644
--- a/store/db/postgres/inbox.go
+++ b/store/db/postgres/inbox.go
@@ -2,6 +2,7 @@ package postgres
 
 import (
 	"context"
+	"database/sql"
 	"strings"
 
 	"github.com/pkg/errors"
@@ -132,3 +133,13 @@ func (d *DB) DeleteInbox(ctx context.Context, delete *store.DeleteInbox) error {
 	}
 	return nil
 }
+
+func vacuumInbox(ctx context.Context, tx *sql.Tx) error {
+	stmt := `DELETE FROM inbox WHERE sender_id NOT IN (SELECT id FROM "user")`
+	_, err := tx.ExecContext(ctx, stmt)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
diff --git a/store/db/postgres/postgres.go b/store/db/postgres/postgres.go
index 212b02fa..57951e0c 100644
--- a/store/db/postgres/postgres.go
+++ b/store/db/postgres/postgres.go
@@ -66,6 +66,9 @@ func (d *DB) Vacuum(ctx context.Context) error {
 	if err := vacuumMemoRelations(ctx, tx); err != nil {
 		return err
 	}
+	if err := vacuumInbox(ctx, tx); err != nil {
+		return err
+	}
 	if err := vacuumTag(ctx, tx); err != nil {
 		// Prevent revive warning.
 		return err
diff --git a/store/db/sqlite/inbox.go b/store/db/sqlite/inbox.go
index 97331c5d..72865b8f 100644
--- a/store/db/sqlite/inbox.go
+++ b/store/db/sqlite/inbox.go
@@ -2,6 +2,7 @@ package sqlite
 
 import (
 	"context"
+	"database/sql"
 	"strings"
 
 	"github.com/pkg/errors"
@@ -123,3 +124,22 @@ func (d *DB) DeleteInbox(ctx context.Context, delete *store.DeleteInbox) error {
 	}
 	return nil
 }
+
+func vacuumInbox(ctx context.Context, tx *sql.Tx) error {
+	stmt := `
+	DELETE FROM
+		inbox
+	WHERE
+		sender_id NOT IN (
+			SELECT
+				id
+			FROM
+				user
+		)`
+	_, err := tx.ExecContext(ctx, stmt)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
diff --git a/store/db/sqlite/sqlite.go b/store/db/sqlite/sqlite.go
index 28e0390d..981a02c8 100644
--- a/store/db/sqlite/sqlite.go
+++ b/store/db/sqlite/sqlite.go
@@ -97,6 +97,9 @@ func vacuumImpl(ctx context.Context, tx *sql.Tx) error {
 	if err := vacuumMemoRelations(ctx, tx); err != nil {
 		return err
 	}
+	if err := vacuumInbox(ctx, tx); err != nil {
+		return err
+	}
 	if err := vacuumTag(ctx, tx); err != nil {
 		// Prevent revive warning.
 		return err