diff --git a/mailserver/sieve.md b/mailserver/sieve.md
index c3cc590..36ea4ec 100644
--- a/mailserver/sieve.md
+++ b/mailserver/sieve.md
@@ -10,7 +10,7 @@ Then it stops processing.
 ```
 require ["fileinto","mailbox","regex","variables"];
 
-if allof (header :regex "to" "^<name>.(.*)@<domain.tld>$")
+if allof (header :regex "to" "^<name>.([0-9a-zA-Z]*)@<domain.tld>$")
 {
         set :lower :upperfirst "target" "${1}";
         fileinto :create "${target}";