add ProxyJump function

outlook-bulk-sender/BulkArchiveMailer.Core/EmailAddressBuilder.cs

@@ -0,0 +1,36 @@
+using System;
+
+namespace BulkArchiveMailer.Core
+{
+    /// <summary>
+    /// Derives the recipient's email address from the login embedded in an
+    /// archive file name. Rule (see repo README/plan, confirmed with the
+    /// operator): a Linux login such as "a-makarov" maps to
+    /// "a.makarov@&lt;domain&gt;" by replacing every hyphen with a dot -
+    /// there is no separate mapping table.
+    ///
+    /// Known accepted limitation (do NOT try to fix this with an override
+    /// mechanism): if a real login contains a literal hyphen that is not
+    /// an initial/surname separator, this produces the wrong local part.
+    /// That is out of scope for this tool - see README.md.
+    /// </summary>
+    public static class EmailAddressBuilder
+    {
+        public static string BuildEmail(string login, string domain)
+        {
+            if (string.IsNullOrWhiteSpace(login))
+            {
+                throw new ArgumentException("login must not be empty.", nameof(login));
+            }
+
+            if (string.IsNullOrWhiteSpace(domain))
+            {
+                throw new ArgumentException("domain must not be empty.", nameof(domain));
+            }
+
+            var localPart = login.Trim().ToLowerInvariant().Replace('-', '.');
+            var cleanDomain = domain.Trim().TrimStart('@');
+            return $"{localPart}@{cleanDomain}";
+        }
+    }
+}