diff --git a/services/socketmap/README.md b/services/socketmap/README.md
index 4aa7971..3b396a0 100644
--- a/services/socketmap/README.md
+++ b/services/socketmap/README.md
@@ -39,11 +39,13 @@ virtual_alias_maps = socketmap:inet:socketmap-server:9100:virtual-aliases
 
 | Map | Purpose | Response |
 |-----|---------|----------|
-| `user-exists` | Validate users via Thunder IDP | `OK email` or `NOTFOUND` |
+| `user-exists` | Validate users and group addresses via Thunder IDP | `OK email` or `NOTFOUND` |
 | `virtual-domains` | Validate domains via Thunder OUs | `OK 1` or `NOTFOUND` |
 | `virtual-aliases` | Resolve aliases | `OK target` or `NOTFOUND` |
 
-**Caching:** Positive results cached for 5 minutes. Negative results NOT cached (new users immediately accessible).
+Group address format: `<groupname>-group@domainname`.
+
+**Caching:** Positive results cached for 5 minutes. Negative results NOT cached (new users/groups immediately accessible).
 
 ## Troubleshooting
 
diff --git a/services/socketmap/internal/handler/user.go b/services/socketmap/internal/handler/user.go
index f801223..02d17f4 100644
--- a/services/socketmap/internal/handler/user.go
+++ b/services/socketmap/internal/handler/user.go
@@ -3,6 +3,7 @@ package handler
 import (
 	"fmt"
 	"log"
+	"strings"
 	"time"
 
 	"socketmap/config"
@@ -41,14 +42,28 @@ func UserExists(email string, cfg *config.Config, cacheManager *cache.Cache) boo
 		log.Printf("    │ Querying IDP...")
 	}
 
-	// Query Thunder IDP for user validation
+	// Query Thunder IDP for user validation first.
 	exists, err := thunder.ValidateUser(email, cfg.ThunderHost, cfg.ThunderPort, cfg.TokenRefreshSeconds)
 	if err != nil {
-		log.Printf("    │ ⚠ IDP query failed: %v", err)
-		log.Printf("    │ User not found - Thunder unavailable")
+		log.Printf("    │ ⚠ User lookup failed: %v", err)
 		exists = false
 	}
 
+	// Treat group addresses as mailbox identities in user-exists map.
+	if !exists && strings.Contains(email, "@") {
+		groupExists, groupErr := thunder.ValidateGroupAddress(email, cfg.ThunderHost, cfg.ThunderPort, cfg.TokenRefreshSeconds)
+		if groupErr != nil {
+			log.Printf("    │ ⚠ Group lookup failed: %v", groupErr)
+		} else if groupExists {
+			log.Printf("    │ ✓ Group found; treating as existing user")
+			exists = true
+		}
+	}
+
+	if !exists {
+		log.Printf("    │ User/group not found - Thunder unavailable or no match")
+	}
+
 	log.Printf("    │ IDP result: exists=%v", exists)
 	
 	// Only cache positive results (exists=true)
diff --git a/services/socketmap/internal/thunder/group.go b/services/socketmap/internal/thunder/group.go
new file mode 100644
index 0000000..88da16c
--- /dev/null
+++ b/services/socketmap/internal/thunder/group.go
@@ -0,0 +1,109 @@
+package thunder
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"strings"
+)
+
+// ValidateGroupAddress checks if an address matches the group pattern and exists in Thunder IDP.
+// Expected format: <group-name>-group@<domain>
+func ValidateGroupAddress(email, host, port string, tokenRefreshSeconds int) (bool, error) {
+	log.Printf("      ┌─ Thunder Group Validation ────")
+	log.Printf("      │ Email: %s", email)
+	defer log.Printf("      └──────────────────────────────")
+
+	parts := strings.Split(email, "@")
+	if len(parts) != 2 {
+		log.Printf("      │ ✗ Invalid email format")
+		return false, nil
+	}
+
+	localPart := parts[0]
+	domain := parts[1]
+
+	if !strings.HasSuffix(localPart, "-group") {
+		log.Printf("      │ ✗ Not a group address")
+		return false, nil
+	}
+
+	groupName := strings.TrimSuffix(localPart, "-group")
+	if groupName == "" {
+		log.Printf("      │ ✗ Empty group name")
+		return false, nil
+	}
+
+	log.Printf("      │ Group: %s", groupName)
+	log.Printf("      │ Domain: %s", domain)
+
+	auth, err := GetAuth(host, port, tokenRefreshSeconds)
+	if err != nil {
+		log.Printf("      │ ⚠ Auth failed: %v", err)
+		return false, err
+	}
+
+	ouID, err := GetOrgUnitIDForDomain(domain, host, port, tokenRefreshSeconds)
+	if err != nil {
+		log.Printf("      │ ⚠ Failed to get OU ID: %v", err)
+		return false, err
+	}
+
+	log.Printf("      │ OU ID: %s", ouID)
+
+	client := GetHTTPClient()
+	escapedGroupName := escapeFilterValue(groupName)
+	filter := fmt.Sprintf("name eq \"%s\"", escapedGroupName)
+
+	baseURL := fmt.Sprintf("https://%s:%s/groups", host, port)
+	req, err := http.NewRequest("GET", baseURL, nil)
+	if err != nil {
+		log.Printf("      │ ✗ Failed to create request: %v", err)
+		return false, err
+	}
+
+	q := req.URL.Query()
+	q.Add("filter", filter)
+	req.URL.RawQuery = q.Encode()
+
+	req.Header.Set("Authorization", "Bearer "+auth.BearerToken)
+	req.Header.Set("Content-Type", "application/json")
+
+	log.Printf("      │ Query: %s", req.URL.String())
+
+	resp, err := client.Do(req)
+	if err != nil {
+		log.Printf("      │ ✗ Request failed: %v", err)
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != 200 {
+		log.Printf("      │ ⚠ Unexpected status: %d", resp.StatusCode)
+		return false, fmt.Errorf("unexpected status: %d", resp.StatusCode)
+	}
+
+	var groupsResp GroupsResponse
+	if err := json.NewDecoder(resp.Body).Decode(&groupsResp); err != nil {
+		log.Printf("      │ ✗ Failed to parse response: %v", err)
+		return false, err
+	}
+
+	log.Printf("      │ Total results: %d", groupsResp.TotalResults)
+
+	if groupsResp.TotalResults == 0 {
+		log.Printf("      │ ✗ Group not found in Thunder")
+		return false, nil
+	}
+
+	for _, group := range groupsResp.Groups {
+		if group.OrganizationUnitID == ouID && group.Name == groupName {
+			log.Printf("      │ ✓ Group found and OU matches")
+			return true, nil
+		}
+	}
+
+	log.Printf("      │ ✗ Group found but OU/name mismatch")
+	return false, nil
+}
\ No newline at end of file
diff --git a/services/socketmap/internal/thunder/types.go b/services/socketmap/internal/thunder/types.go
index e27e6a5..1d033fd 100644
--- a/services/socketmap/internal/thunder/types.go
+++ b/services/socketmap/internal/thunder/types.go
@@ -48,3 +48,19 @@ type User struct {
 	Type             string                 `json:"type"`
 	Attributes       map[string]interface{} `json:"attributes"`
 }
+
+// GroupsResponse represents the response from Thunder Groups API
+type GroupsResponse struct {
+	TotalResults int           `json:"totalResults"`
+	StartIndex   int           `json:"startIndex"`
+	Count        int           `json:"count"`
+	Groups       []Group       `json:"groups"`
+	Links        []interface{} `json:"links"`
+}
+
+// Group represents a Thunder group
+type Group struct {
+	ID                 string `json:"id"`
+	Name               string `json:"name"`
+	OrganizationUnitID string `json:"organizationUnitId"`
+}