diff --git a/app/src/main/java/eu/faircode/email/AdapterMessage.java b/app/src/main/java/eu/faircode/email/AdapterMessage.java
index bffbd59c21..15067b7f3e 100644
--- a/app/src/main/java/eu/faircode/email/AdapterMessage.java
+++ b/app/src/main/java/eu/faircode/email/AdapterMessage.java
@@ -2649,9 +2649,9 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
                     signers.append(signer);
                     for (Address a : envelop) {
                         String domain = UriHelper.getEmailDomain(((InternetAddress) a).getAddress());
-                        if (domain != null && Objects.equals(
-                                UriHelper.getRootDomain(context, signer),
-                                UriHelper.getRootDomain(context, domain))) {
+                        if (signer != null && domain != null && Objects.equals(
+                                UriHelper.getRootDomain(context, signer.toLowerCase(Locale.ROOT)),
+                                UriHelper.getRootDomain(context, domain.toLowerCase(Locale.ROOT)))) {
                             signers.setSpan(new ForegroundColorSpan(textColorLink), start, signers.length(), 0);
                             known_signer = true;
                             break;
diff --git a/app/src/main/java/eu/faircode/email/MessageHelper.java b/app/src/main/java/eu/faircode/email/MessageHelper.java
index 08427c4a6e..c0479a3243 100644
--- a/app/src/main/java/eu/faircode/email/MessageHelper.java
+++ b/app/src/main/java/eu/faircode/email/MessageHelper.java
@@ -2648,15 +2648,14 @@ public class MessageHelper {
             envelop.addAll(Arrays.asList(from));
         if (smtp_from != null)
             envelop.addAll(Arrays.asList(smtp_from));
-        for (String signer : signers) {
+        for (String signer : signers)
             for (Address a : envelop) {
                 String domain = UriHelper.getEmailDomain(((InternetAddress) a).getAddress());
-                if (domain != null && Objects.equals(
-                        UriHelper.getRootDomain(context, signer),
-                        UriHelper.getRootDomain(context, domain)))
+                if (signer != null && domain != null && Objects.equals(
+                        UriHelper.getRootDomain(context, signer.toLowerCase(Locale.ROOT)),
+                        UriHelper.getRootDomain(context, domain.toLowerCase(Locale.ROOT))))
                     return true;
             }
-        }
         return false;
     }