@@ 6,19 6,59 @@ import (
 	"golang.org/x/exp/slices"
 )
 
-// EmailSafe will verify an email domain is not in the blacklist
-func EmailSafe(email string) bool {
+// EmailSplit will return the username and domain parts of an email address
+func EmailSplit(email string) (string, string) {
 	at := strings.LastIndex(email, "@")
-	if at <= 0 {
-		return false
+	if at > 0 {
+		return email[:at], email[at+1:]
 	}
-	domain := email[at+1:]
-	return true != slices.Contains(emailBlacklist, domain)
+	return email, ""
+}
+
+// BlacklistValidator is a checker to validate input against blacklists
+type BlacklistValidator struct{}
+
+func (b *BlacklistValidator) checkSafe(listing []string, value string) bool {
+	return true != slices.Contains(listing, value)
+}
+
+func (b *BlacklistValidator) emailSafe(listing []string, value string) bool {
+	_, domain := EmailSplit(value)
+	return b.checkSafe(listing, domain)
+}
+
+// EmailSafe will verify an email domain is not in the default blacklist
+func (b *BlacklistValidator) EmailSafe(email string) bool {
+	return b.emailSafe(emailBlacklist, email)
 }
 
-// UsernameSafe will verify a username is not in the blacklist
-func UsernameSafe(username string) bool {
-	return true != slices.Contains(usernameBlacklist, username)
+// EmailSafePlus will concatenate given list to default `emailBlacklist` and check
+// the given email to see if the domain is in either list.
+func (b *BlacklistValidator) EmailSafePlus(listing []string, email string) bool {
+	return b.emailSafe(append(emailBlacklist, listing...), email)
+}
+
+// EmailSafeOnly will only check the given email domain against the provided list.
+// This will exclude the default `emailBlacklist`
+func (b *BlacklistValidator) EmailSafeOnly(listing []string, email string) bool {
+	return b.emailSafe(listing, email)
+}
+
+// UsernameSafe will verify a username is not in the default blacklist
+func (b *BlacklistValidator) UsernameSafe(username string) bool {
+	return b.checkSafe(usernameBlacklist, username)
+}
+
+// UsernameSafePlus will concatenate given list to default `usernameBlacklist` and check
+// the given email to see if the domain is in either list.
+func (b *BlacklistValidator) UsernameSafePlus(listing []string, email string) bool {
+	return b.checkSafe(append(usernameBlacklist, listing...), email)
+}
+
+// UsernameSafeOnly will only check the given email domain against the provided list.
+// This will exclude the default `emailBlacklist`
+func (b *BlacklistValidator) UsernameSafeOnly(listing []string, email string) bool {
+	return b.checkSafe(listing, email)
 }
 
 // https://git.sr.ht/~sircmpwn/meta.sr.ht/tree/master/item/metasrht/blacklist.py