diff --git a/config/config.go b/config/config.go
index 00e2585..684c49c 100644
--- a/config/config.go
+++ b/config/config.go
@@ -262,7 +262,7 @@ type TransportSocks struct {
 
 type Domain struct {
 	Description                string  `sconf:"optional" sconf-doc:"Free-form description of domain."`
-	ClientSettingsDomain       string  `sconf:"optional" sconf-doc:"Hostname for client settings instead of the mail server hostname. E.g. mail.<domain>. For future migration to another mail operator without requiring all clients to update their settings, it is convenient to have client settings that reference a subdomain of the hosted domain instead of the hostname of the server where the mail is currently hosted. If empty, the hostname of the mail server is used for client configurations."`
+	ClientSettingsDomain       string  `sconf:"optional" sconf-doc:"Hostname for client settings instead of the mail server hostname. E.g. mail.<domain>. For future migration to another mail operator without requiring all clients to update their settings, it is convenient to have client settings that reference a subdomain of the hosted domain instead of the hostname of the server where the mail is currently hosted. If empty, the hostname of the mail server is used for client configurations. Unicode name."`
 	LocalpartCatchallSeparator string  `sconf:"optional" sconf-doc:"If not empty, only the string before the separator is used to for email delivery decisions. For example, if set to \"+\", you+anything@example.com will be delivered to you@example.com."`
 	LocalpartCaseSensitive     bool    `sconf:"optional" sconf-doc:"If set, upper/lower case is relevant for email delivery."`
 	DKIM                       DKIM    `sconf:"optional" sconf-doc:"With DKIM signing, a domain is taking responsibility for (content of) emails it sends, letting receiving mail servers build up a (hopefully positive) reputation of the domain, which can help with mail delivery."`
diff --git a/config/doc.go b/config/doc.go
index 6f83282..49d3095 100644
--- a/config/doc.go
+++ b/config/doc.go
@@ -686,7 +686,7 @@ See https://pkg.go.dev/github.com/mjl-/sconf for details.
 			# all clients to update their settings, it is convenient to have client settings
 			# that reference a subdomain of the hosted domain instead of the hostname of the
 			# server where the mail is currently hosted. If empty, the hostname of the mail
-			# server is used for client configurations. (optional)
+			# server is used for client configurations. Unicode name. (optional)
 			ClientSettingsDomain:
 
 			# If not empty, only the string before the separator is used to for email delivery
diff --git a/mox-/config.go b/mox-/config.go
index fd8a286..fb62fcc 100644
--- a/mox-/config.go
+++ b/mox-/config.go
@@ -520,7 +520,7 @@ func PrepareStaticConfig(ctx context.Context, log mlog.Log, configFile string, c
 	if err != nil {
 		addErrorf("parsing hostname: %s", err)
 	} else if hostname.Name() != c.Hostname {
-		addErrorf("hostname must be in IDNA form %q", hostname.Name())
+		addErrorf("hostname must be in unicode form %q instead of %q", hostname.Name(), c.Hostname)
 	}
 	c.HostnameDomain = hostname
 
@@ -1085,7 +1085,7 @@ func prepareDynamicConfig(ctx context.Context, log mlog.Log, dynamicPath string,
 		if err != nil {
 			addErrorf("bad domain %q: %s", d, err)
 		} else if dnsdomain.Name() != d {
-			addErrorf("domain %s must be specified in IDNA form, %s", d, dnsdomain.Name())
+			addErrorf("domain %s must be specified in unicode form, %s", d, dnsdomain.Name())
 		}
 
 		domain.Domain = dnsdomain
@@ -1108,7 +1108,7 @@ func prepareDynamicConfig(ctx context.Context, log mlog.Log, dynamicPath string,
 			if err != nil {
 				addErrorf("bad selector %q: %s", name, err)
 			} else if seld.Name() != name {
-				addErrorf("selector %q must be specified in IDNA form, %q", name, seld.Name())
+				addErrorf("selector %q must be specified in unicode form, %q", name, seld.Name())
 			}
 			sel.Domain = seld