diff --git a/plugins/viewhtml/plugin.go b/plugins/viewhtml/plugin.go
index b34372f..1007d4a 100644
--- a/plugins/viewhtml/plugin.go
+++ b/plugins/viewhtml/plugin.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"git.sr.ht/~emersion/koushin"
+	koushinbase "git.sr.ht/~emersion/koushin/plugins/base"
 	"github.com/labstack/echo/v4"
 )
 
@@ -20,6 +21,17 @@ var (
 func init() {
 	p := koushin.GoPlugin{Name: "viewhtml"}
 
+	p.Inject("message.html", func(ctx *koushin.Context, _data koushin.RenderData) error {
+		data := _data.(*koushinbase.MessageRenderData)
+		data.Extra["RemoteResourcesAllowed"] = ctx.QueryParam("allow-remote-resources") == "1"
+		hasRemoteResources := false
+		if v := ctx.Get("viewhtml.hasRemoteResources"); v != nil {
+			hasRemoteResources = v.(bool)
+		}
+		data.Extra["HasRemoteResources"] = hasRemoteResources
+		return nil
+	})
+
 	p.GET("/proxy", func(ctx *koushin.Context) error {
 		if !proxyEnabled {
 			return echo.NewHTTPError(http.StatusForbidden, "proxy disabled")
diff --git a/plugins/viewhtml/sanitize.go b/plugins/viewhtml/sanitize.go
index a931fe1..ba2aca9 100644
--- a/plugins/viewhtml/sanitize.go
+++ b/plugins/viewhtml/sanitize.go
@@ -71,7 +71,9 @@ var allowedStyles = map[string]bool{
 }
 
 type sanitizer struct {
-	msg *koushinbase.IMAPMessage
+	msg                  *koushinbase.IMAPMessage
+	allowRemoteResources bool
+	hasRemoteResources   bool
 }
 
 func (san *sanitizer) sanitizeImageURL(src string) string {
@@ -94,7 +96,9 @@ func (san *sanitizer) sanitizeImageURL(src string) string {
 
 		return part.URL(true).String()
 	case "https":
-		if !proxyEnabled {
+		san.hasRemoteResources = true
+
+		if !proxyEnabled || !san.allowRemoteResources {
 			return "about:blank"
 		}
 
diff --git a/plugins/viewhtml/viewer.go b/plugins/viewhtml/viewer.go
index 47f5eea..abc9f2d 100644
--- a/plugins/viewhtml/viewer.go
+++ b/plugins/viewhtml/viewer.go
@@ -25,6 +25,8 @@ var tpl = template.Must(template.New("view-html.html").Parse(tplSrc))
 type viewer struct{}
 
 func (viewer) ViewMessagePart(ctx *koushin.Context, msg *koushinbase.IMAPMessage, part *message.Entity) (interface{}, error) {
+	allowRemoteResources := ctx.QueryParam("allow-remote-resources") == "1"
+
 	mimeType, _, err := part.Header.ContentType()
 	if err != nil {
 		return nil, err
@@ -38,12 +40,17 @@ func (viewer) ViewMessagePart(ctx *koushin.Context, msg *koushinbase.IMAPMessage
 		return nil, fmt.Errorf("failed to read part body: %v", err)
 	}
 
-	san := sanitizer{msg}
+	san := sanitizer{
+		msg:                  msg,
+		allowRemoteResources: allowRemoteResources,
+	}
 	body, err = san.sanitizeHTML(body)
 	if err != nil {
 		return nil, fmt.Errorf("failed to sanitize HTML part: %v", err)
 	}
 
+	ctx.Set("viewhtml.hasRemoteResources", san.hasRemoteResources)
+
 	var buf bytes.Buffer
 	err = tpl.Execute(&buf, string(body))
 	if err != nil {
diff --git a/themes/sourcehut/message.html b/themes/sourcehut/message.html
index fb38932..17f5976 100644
--- a/themes/sourcehut/message.html
+++ b/themes/sourcehut/message.html
@@ -99,6 +99,13 @@
         {{end}}
       </ul>
 
+      {{if and .Extra.HasRemoteResources (not .Extra.RemoteResourcesAllowed)}}
+        <p class="alert alert-info">
+          This message contains remote content.
+          <a href="?part={{.PartPath}}&allow-remote-resources=1" class="alert-link">Load</a>
+        </p>
+      {{end}}
+
       {{if .View}}
         {{.View}}
       {{else}}