pkgs: mailnix: Improve alias-validation to also regard catch-all aliases and domain-aliases

pkgs/mailnix/src/config.rs

@@ -132,6 +132,34 @@ impl Config {
         Ok(())
     }
 
+    fn is_valid_destination(&self, address: &String) -> bool {
+        if self.accounts.contains_key(address) {
+            return true;
+        }
+
+        // There is no explicit account matching 'address'. However, 'address' may still be
+        // implicitly valid due to the existence of a catchall-alias or the domain being aliased.
+        let (local_part, domain) = parse_address(address).unwrap();
+        if let Some(dests) = self.aliases.get(&domain) {
+            if dests.iter().filter(|dest| !is_domain(dest)).count() > 0 {
+                // At least one explicit catchall-address exists!
+                return true;
+            }
+            // At this point, we need to (recursively) iterate over domain-aliases to check whether
+            // there is an exact match (or a catchall-alias for the aliased domain).
+            for dest in dests.iter().filter(|addr| is_domain(addr)) {
+                let aliased_addr = format!("{local_part}@{dest}");
+                // FIXME: This current implementation may not terminate if the configured aliases
+                // contain a loop!
+                if self.is_valid_destination(&aliased_addr) {
+                    return true;
+                }
+            }
+        }
+        // alias destination is not valid
+        false
+    }
+
     pub fn check(&self) -> Result<(), Box<dyn Error>> {
         // check whether all account domains exist
         for name in self.accounts.keys() {
@@ -149,7 +177,7 @@ impl Config {
             for dest in dests.iter() {
                 if is_domain(dest) && !self.domains.contains(dest) {
                     panic!("Aliased dest-domain \"{dest}\" does not exist");
-                } else if !is_domain(dest) && !self.accounts.contains_key(dest) {
+                } else if !is_domain(dest) && !self.is_valid_destination(dest) {
                     panic!("Aliased dest-account \"{dest}\" does not exist");
                 }
             }