diff --git a/crates/directory/src/backend/internal/lookup.rs b/crates/directory/src/backend/internal/lookup.rs
index 01ce9f1a..c8e1ec41 100644
--- a/crates/directory/src/backend/internal/lookup.rs
+++ b/crates/directory/src/backend/internal/lookup.rs
@@ -13,6 +13,7 @@ use store::{
     write::{DirectoryClass, ValueClass},
 };
 use trc::AddContext;
+use utils::DomainPart;
 
 #[allow(async_fn_in_trait)]
 pub trait DirectoryStore: Sync + Send {
@@ -117,7 +118,7 @@ impl DirectoryStore for Store {
 
     async fn vrfy(&self, address: &str) -> trc::Result<Vec<String>> {
         let mut results = Vec::new();
-        let address = address.split('@').next().unwrap_or(address);
+        let address = address.try_local_part().unwrap_or(address);
         if address.len() > 3 {
             self.iterate(
                 IterateParams::new(
@@ -129,7 +130,7 @@ impl DirectoryStore for Store {
                 |key, value| {
                     let key =
                         std::str::from_utf8(key.get(1..).unwrap_or_default()).unwrap_or_default();
-                    if key.split('@').next().unwrap_or(key).contains(address)
+                    if key.try_local_part().unwrap_or(key).contains(address)
                         && PrincipalInfo::deserialize(value)
                             .caused_by(trc::location!())?
                             .typ
diff --git a/crates/directory/src/backend/internal/manage.rs b/crates/directory/src/backend/internal/manage.rs
index 77e1a37c..187f2889 100644
--- a/crates/directory/src/backend/internal/manage.rs
+++ b/crates/directory/src/backend/internal/manage.rs
@@ -27,7 +27,7 @@ use store::{
 };
 use trc::AddContext;
 use types::collection::Collection;
-use utils::sanitize_email;
+use utils::{DomainPart, sanitize_email};
 
 #[derive(Debug, Default, serde::Serialize, serde::Deserialize)]
 pub struct PrincipalList<T> {
@@ -354,7 +354,7 @@ impl ManageDirectory for Store {
             principal_create.tenant = tenant_id.into();
 
             if !matches!(principal_create.typ, Type::Tenant | Type::Domain) {
-                if let Some(domain) = name.split('@').nth(1)
+                if let Some(domain) = name.try_domain_part()
                     && self
                         .get_principal_info(domain)
                         .await
@@ -523,7 +523,7 @@ impl ManageDirectory for Store {
                 if self.rcpt(&email).await.caused_by(trc::location!())? != RcptType::Invalid {
                     return Err(err_exists(PrincipalField::Emails, email.to_string()));
                 }
-                if let Some(domain) = email.split('@').nth(1)
+                if let Some(domain) = email.try_domain_part()
                     && valid_domains.insert(domain.into())
                 {
                     self.get_principal_info(domain)
@@ -1003,7 +1003,7 @@ impl ManageDirectory for Store {
                         if tenant_id.is_some()
                             && !matches!(principal_type, Type::Tenant | Type::Domain)
                         {
-                            if let Some(domain) = new_name.split('@').nth(1)
+                            if let Some(domain) = new_name.try_domain_part()
                                 && self
                                     .get_principal_info(domain)
                                     .await
@@ -2401,7 +2401,7 @@ impl ValidateDirectory for Store {
     ) -> trc::Result<()> {
         if self.rcpt(email).await.caused_by(trc::location!())? != RcptType::Invalid {
             Err(err_exists(PrincipalField::Emails, email.to_string()))
-        } else if let Some(domain) = email.split('@').nth(1) {
+        } else if let Some(domain) = email.try_domain_part() {
             match self
                 .get_principal_info(domain)
                 .await
diff --git a/crates/imap-proto/src/protocol/fetch.rs b/crates/imap-proto/src/protocol/fetch.rs
index 6e0be0dc..61338c54 100644
--- a/crates/imap-proto/src/protocol/fetch.rs
+++ b/crates/imap-proto/src/protocol/fetch.rs
@@ -261,7 +261,7 @@ impl EmailAddress<'_> {
             &self.address
         };
 
-        if let Some((local, host)) = addr.split_once('@') {
+        if let Some((local, host)) = addr.rsplit_once('@') {
             quoted_or_literal_string(buf, local);
             buf.push(b' ');
             quoted_or_literal_string(buf, host);
diff --git a/crates/smtp/src/core/mod.rs b/crates/smtp/src/core/mod.rs
index 6daf546c..82202680 100644
--- a/crates/smtp/src/core/mod.rs
+++ b/crates/smtp/src/core/mod.rs
@@ -4,31 +4,26 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use std::{
-    hash::Hash,
-    net::IpAddr,
-    sync::Arc,
-    time::{Duration, Instant},
-};
-
+use crate::{inbound::auth::SaslToken, queue::QueueId};
 use common::{
     Inner, Server,
     auth::AccessToken,
     config::smtp::auth::VerifyStrategy,
     listener::{ServerInstance, asn::AsnGeoLookupResult},
 };
-
 use directory::Directory;
 use mail_auth::{IprevOutput, SpfOutput};
 use smtp_proto::request::receiver::{
     BdatReceiver, DataReceiver, DummyDataReceiver, DummyLineReceiver, LineReceiver, RequestReceiver,
 };
-use tokio::io::{AsyncRead, AsyncWrite};
-
-use crate::{
-    inbound::auth::SaslToken,
-    queue::{DomainPart, QueueId},
+use std::{
+    hash::Hash,
+    net::IpAddr,
+    sync::Arc,
+    time::{Duration, Instant},
 };
+use tokio::io::{AsyncRead, AsyncWrite};
+use utils::DomainPart;
 
 pub mod params;
 pub mod throttle;
diff --git a/crates/smtp/src/inbound/data.rs b/crates/smtp/src/inbound/data.rs
index fd30a35d..00763140 100644
--- a/crates/smtp/src/inbound/data.rs
+++ b/crates/smtp/src/inbound/data.rs
@@ -8,10 +8,7 @@ use super::{ArcSeal, AuthResult, DkimSign};
 use crate::{
     core::{Session, SessionAddress, State},
     inbound::milter::Modification,
-    queue::{
-        self, DomainPart, Message, MessageSource, MessageWrapper, QueueEnvelope,
-        quota::HasQueueQuota,
-    },
+    queue::{self, Message, MessageSource, MessageWrapper, QueueEnvelope, quota::HasQueueQuota},
     reporting::analysis::AnalyzeReport,
     scripts::ScriptResult,
 };
@@ -44,7 +41,7 @@ use std::{
     time::{Instant, SystemTime},
 };
 use trc::SmtpEvent;
-use utils::config::Rate;
+use utils::{DomainPart, config::Rate};
 
 impl<T: SessionStream> Session<T> {
     pub async fn queue_message(&mut self) -> Cow<'static, [u8]> {
diff --git a/crates/smtp/src/inbound/mail.rs b/crates/smtp/src/inbound/mail.rs
index 29aa6637..00c83824 100644
--- a/crates/smtp/src/inbound/mail.rs
+++ b/crates/smtp/src/inbound/mail.rs
@@ -6,7 +6,6 @@
 
 use crate::{
     core::{Session, SessionAddress},
-    queue::DomainPart,
     scripts::ScriptResult,
 };
 use common::{config::smtp::session::Stage, listener::SessionStream, scripts::ScriptModification};
@@ -17,7 +16,7 @@ use std::{
     time::{Duration, Instant, SystemTime},
 };
 use trc::SmtpEvent;
-use utils::config::Rate;
+use utils::{DomainPart, config::Rate};
 
 impl<T: SessionStream> Session<T> {
     pub async fn handle_mail_from(&mut self, from: MailFrom<Cow<'_, str>>) -> Result<(), ()> {
diff --git a/crates/smtp/src/inbound/milter/message.rs b/crates/smtp/src/inbound/milter/message.rs
index 6d221e67..f087aca0 100644
--- a/crates/smtp/src/inbound/milter/message.rs
+++ b/crates/smtp/src/inbound/milter/message.rs
@@ -4,26 +4,22 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use std::{borrow::Cow, time::Instant};
-
+use super::{Action, Error, Macros, Modification};
+use crate::{
+    core::{Session, SessionAddress, SessionData},
+    inbound::{FilterResponse, milter::MilterClient},
+};
 use common::{
     DAEMON_NAME,
     config::smtp::session::{Milter, Stage},
     listener::SessionStream,
 };
-
 use mail_auth::AuthenticatedMessage;
 use smtp_proto::{IntoString, request::parser::Rfc5321Parser};
+use std::{borrow::Cow, time::Instant};
 use tokio::io::{AsyncRead, AsyncWrite};
 use trc::MilterEvent;
-
-use crate::{
-    core::{Session, SessionAddress, SessionData},
-    inbound::{FilterResponse, milter::MilterClient},
-    queue::DomainPart,
-};
-
-use super::{Action, Error, Macros, Modification};
+use utils::DomainPart;
 
 enum Rejection {
     Action(Action),
diff --git a/crates/smtp/src/inbound/rcpt.rs b/crates/smtp/src/inbound/rcpt.rs
index b1300c1c..ab292e28 100644
--- a/crates/smtp/src/inbound/rcpt.rs
+++ b/crates/smtp/src/inbound/rcpt.rs
@@ -4,24 +4,21 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use std::borrow::Cow;
-
+use crate::{
+    core::{Session, SessionAddress},
+    scripts::ScriptResult,
+};
 use common::{
     KV_GREYLIST, config::smtp::session::Stage, listener::SessionStream, scripts::ScriptModification,
 };
-
 use directory::backend::RcptType;
 use smtp_proto::{
     RCPT_NOTIFY_DELAY, RCPT_NOTIFY_FAILURE, RCPT_NOTIFY_NEVER, RCPT_NOTIFY_SUCCESS, RcptTo,
 };
+use std::borrow::Cow;
 use store::dispatch::lookup::KeyValue;
 use trc::{SecurityEvent, SmtpEvent};
-
-use crate::{
-    core::{Session, SessionAddress},
-    queue::DomainPart,
-    scripts::ScriptResult,
-};
+use utils::DomainPart;
 
 impl<T: SessionStream> Session<T> {
     pub async fn handle_rcpt_to(&mut self, to: RcptTo<Cow<'_, str>>) -> Result<(), ()> {
diff --git a/crates/smtp/src/queue/mod.rs b/crates/smtp/src/queue/mod.rs
index 991440a2..33003674 100644
--- a/crates/smtp/src/queue/mod.rs
+++ b/crates/smtp/src/queue/mod.rs
@@ -17,6 +17,7 @@ use std::{
 };
 use store::write::now;
 use types::blob_hash::BlobHash;
+use utils::DomainPart;
 
 pub mod dsn;
 pub mod manager;
@@ -460,38 +461,6 @@ impl InstantFromTimestamp for u64 {
     }
 }
 
-pub trait DomainPart {
-    fn to_lowercase_domain(&self) -> String;
-    fn domain_part(&self) -> &str;
-}
-
-impl<T: AsRef<str>> DomainPart for T {
-    fn to_lowercase_domain(&self) -> String {
-        let address = self.as_ref();
-        if let Some((local, domain)) = address.rsplit_once('@') {
-            let mut address = String::with_capacity(address.len());
-            address.push_str(local);
-            address.push('@');
-            for ch in domain.chars() {
-                for ch in ch.to_lowercase() {
-                    address.push(ch);
-                }
-            }
-            address
-        } else {
-            address.to_string()
-        }
-    }
-
-    #[inline(always)]
-    fn domain_part(&self) -> &str {
-        self.as_ref()
-            .rsplit_once('@')
-            .map(|(_, d)| d)
-            .unwrap_or_default()
-    }
-}
-
 impl Display for Error {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
diff --git a/crates/smtp/src/queue/quota.rs b/crates/smtp/src/queue/quota.rs
index cb9e21de..f37fb007 100644
--- a/crates/smtp/src/queue/quota.rs
+++ b/crates/smtp/src/queue/quota.rs
@@ -5,10 +5,7 @@
  */
 
 use super::{QueueEnvelope, QuotaKey, Status};
-use crate::{
-    core::throttle::NewKey,
-    queue::{DomainPart, MessageWrapper},
-};
+use crate::{core::throttle::NewKey, queue::MessageWrapper};
 use ahash::AHashSet;
 use common::{Server, config::smtp::queue::QueueQuota, expr::functions::ResolveVariable};
 use std::future::Future;
@@ -17,6 +14,7 @@ use store::{
     write::{BatchBuilder, QueueClass, ValueClass},
 };
 use trc::QueueEvent;
+use utils::DomainPart;
 
 pub trait HasQueueQuota: Sync + Send {
     fn has_quota(&self, message: &mut MessageWrapper) -> impl Future<Output = bool> + Send;
diff --git a/crates/smtp/src/queue/spool.rs b/crates/smtp/src/queue/spool.rs
index 8a107f37..3e0ec169 100644
--- a/crates/smtp/src/queue/spool.rs
+++ b/crates/smtp/src/queue/spool.rs
@@ -10,8 +10,8 @@ use super::{
 };
 use crate::queue::manager::{LockedMessage, Queue};
 use crate::queue::{
-    DomainPart, FROM_AUTHENTICATED, FROM_AUTOGENERATED, FROM_DSN, FROM_REPORT,
-    FROM_UNAUTHENTICATED, FROM_UNAUTHENTICATED_DMARC, MessageWrapper,
+    FROM_AUTHENTICATED, FROM_AUTOGENERATED, FROM_DSN, FROM_REPORT, FROM_UNAUTHENTICATED,
+    FROM_UNAUTHENTICATED_DMARC, MessageWrapper,
 };
 use common::config::smtp::queue::QueueName;
 use common::ipc::QueueEvent;
@@ -28,6 +28,7 @@ use store::write::{
 use store::{Deserialize, IterateParams, Serialize, SerializeInfallible, U64_LEN, ValueKey};
 use trc::{AddContext, ServerEvent};
 use types::blob_hash::BlobHash;
+use utils::DomainPart;
 
 pub const LOCK_EXPIRY: u64 = 10 * 60; // 10 minutes
 pub const QUEUE_REFRESH: u64 = 5 * 60; // 5 minutes
diff --git a/crates/smtp/src/reporting/dmarc.rs b/crates/smtp/src/reporting/dmarc.rs
index b4cdfbf8..154858b7 100644
--- a/crates/smtp/src/reporting/dmarc.rs
+++ b/crates/smtp/src/reporting/dmarc.rs
@@ -5,11 +5,7 @@
  */
 
 use super::{AggregateTimestamp, SerializedSize};
-use crate::{
-    core::Session,
-    queue::{DomainPart, RecipientDomain},
-    reporting::SmtpReporting,
-};
+use crate::{core::Session, queue::RecipientDomain, reporting::SmtpReporting};
 use ahash::AHashMap;
 use common::{
     Server,
@@ -31,7 +27,7 @@ use store::{
     write::{AlignedBytes, Archive, Archiver, BatchBuilder, QueueClass, ReportEvent, ValueClass},
 };
 use trc::{AddContext, OutgoingReportEvent};
-use utils::config::Rate;
+use utils::{DomainPart, config::Rate};
 
 #[derive(
     Debug,
diff --git a/crates/smtp/src/scripts/envelope.rs b/crates/smtp/src/scripts/envelope.rs
index 980594f2..d6e9bbd1 100644
--- a/crates/smtp/src/scripts/envelope.rs
+++ b/crates/smtp/src/scripts/envelope.rs
@@ -9,11 +9,9 @@ use smtp_proto::{
     MAIL_BY_NOTIFY, MAIL_BY_RETURN, MAIL_BY_TRACE, MAIL_RET_FULL, MAIL_RET_HDRS, RCPT_NOTIFY_DELAY,
     RCPT_NOTIFY_FAILURE, RCPT_NOTIFY_NEVER, RCPT_NOTIFY_SUCCESS,
 };
+use utils::DomainPart;
 
-use crate::{
-    core::{SessionAddress, SessionData},
-    queue::DomainPart,
-};
+use crate::core::{SessionAddress, SessionData};
 
 impl SessionData {
     pub fn apply_envelope_modification(&mut self, envelope: Envelope, value: String) {
diff --git a/crates/utils/src/lib.rs b/crates/utils/src/lib.rs
index 2b7b9a4d..4957bee6 100644
--- a/crates/utils/src/lib.rs
+++ b/crates/utils/src/lib.rs
@@ -164,6 +164,50 @@ pub fn rustls_client_config(allow_invalid_certs: bool) -> ClientConfig {
     }
 }
 
+pub trait DomainPart {
+    fn to_lowercase_domain(&self) -> String;
+    fn domain_part(&self) -> &str;
+    fn try_domain_part(&self) -> Option<&str>;
+    fn try_local_part(&self) -> Option<&str>;
+}
+
+impl<T: AsRef<str>> DomainPart for T {
+    fn to_lowercase_domain(&self) -> String {
+        let address = self.as_ref();
+        if let Some((local, domain)) = address.rsplit_once('@') {
+            let mut address = String::with_capacity(address.len());
+            address.push_str(local);
+            address.push('@');
+            for ch in domain.chars() {
+                for ch in ch.to_lowercase() {
+                    address.push(ch);
+                }
+            }
+            address
+        } else {
+            address.to_string()
+        }
+    }
+
+    #[inline(always)]
+    fn try_domain_part(&self) -> Option<&str> {
+        self.as_ref().rsplit_once('@').map(|(_, d)| d)
+    }
+
+    #[inline(always)]
+    fn try_local_part(&self) -> Option<&str> {
+        self.as_ref().rsplit_once('@').map(|(l, _)| l)
+    }
+
+    #[inline(always)]
+    fn domain_part(&self) -> &str {
+        self.as_ref()
+            .rsplit_once('@')
+            .map(|(_, d)| d)
+            .unwrap_or_default()
+    }
+}
+
 #[derive(Debug)]
 struct DummyVerifier;