diff --git a/packages/alias-to-sieve/src/lib.rs b/packages/alias-to-sieve/src/lib.rs
index 35ebea2..6622a8a 100644
--- a/packages/alias-to-sieve/src/lib.rs
+++ b/packages/alias-to-sieve/src/lib.rs
@@ -12,7 +12,7 @@ pub struct AliasFile {
     pub default_domain: FQDN,
 }
 
-#[derive(PartialEq, Eq, Clone)]
+#[derive(PartialEq, Eq, Clone, Debug)]
 pub struct OrdEmailAddress(EmailAddress);
 
 impl PartialOrd for OrdEmailAddress {
@@ -48,6 +48,11 @@ pub fn parse_alias_to_map(alias_files: Vec<AliasFile>) -> Result<AliasMap, Box<d
                 continue;
             }
 
+            if destination.contains('\'') {
+                return Err(format!("Mailaddress {destination} contains an apostrophe which is not allowed by HRZ.")
+                .into());
+            }
+
             let redirects: Vec<OrdEmailAddress> = line
                 .split_at(line.find(char::is_whitespace).unwrap_or(0))
                 .1
@@ -95,7 +100,7 @@ pub fn parse_alias_to_map(alias_files: Vec<AliasFile>) -> Result<AliasMap, Box<d
         }
     }
     if iterations == max_iterations {
-        return Err(String::from("Possibly infinite recursion detected in parse_alias_map. Did not terminate after {max_iterations} rounds.").into());
+        return Err(format!("Possibly infinite recursion detected in parse_alias_map. Did not terminate after {max_iterations} rounds.").into());
     }
     Ok(redirect_map)
 }
@@ -190,6 +195,15 @@ mod tests {
         assert!(result.is_err());
     }
 
+    #[test]
+    fn apostrophe_detection() {
+        let result = parse_alias_to_map(vec![AliasFile {
+            content: read_lines("testdata/apostrophe.aliases").unwrap(),
+            default_domain: FQDN::from_str("example.com").unwrap(),
+        }]);
+        assert!(result.is_err());
+    }
+
     #[test]
     fn basic_parsing() {
         let result = parse_alias_to_map(vec![AliasFile {
diff --git a/packages/alias-to-sieve/testdata/apostrophe.aliases b/packages/alias-to-sieve/testdata/apostrophe.aliases
new file mode 100644
index 0000000..37a6f91
--- /dev/null
+++ b/packages/alias-to-sieve/testdata/apostrophe.aliases
@@ -0,0 +1,2 @@
+# Apostrophes are not allowed by HRZ
+'orga me@example.com