Clippy fixes

crates/smtp/src/outbound/lookup.rs

@@ -194,7 +194,7 @@ pub trait ToNextHop {
         &'x self,
         domain: &'y str,
         max_mx: usize,
-    ) -> Option<Vec<NextHop<'_>>>;
+    ) -> Option<Vec<NextHop<'x>>>;
 }
 
 impl ToNextHop for Vec<MX> {
@@ -202,7 +202,7 @@ impl ToNextHop for Vec<MX> {
         &'x self,
         domain: &'y str,
         max_mx: usize,
-    ) -> Option<Vec<NextHop<'_>>> {
+    ) -> Option<Vec<NextHop<'x>>> {
         if !self.is_empty() {
             // Obtain max number of MX hosts to process
             let mut remote_hosts = Vec::with_capacity(max_mx);

crates/smtp/src/outbound/mod.rs

@@ -218,7 +218,7 @@ pub enum NextHop<'x> {
     MX(&'x str),
 }
 
-impl<'x> NextHop<'x> {
+impl NextHop<'_> {
     #[inline(always)]
     fn hostname(&self) -> &str {
         match self {