diff --git a/docs/documentation/configuration/overview.md b/docs/documentation/configuration/overview.md
index 0345338..44ce206 100644
--- a/docs/documentation/configuration/overview.md
+++ b/docs/documentation/configuration/overview.md
@@ -72,6 +72,7 @@ mail:
   auth_type: plain
   from: Wireguard Portal <noreply@wireguard.local>
   link_only: false
+  allow_peer_email: false
 
 auth:
   oidc: []
@@ -380,7 +381,9 @@ Controls how WireGuard Portal collects and reports usage statistics, including p
 
 ## Mail
 
-Options for configuring email notifications or sending peer configurations via email.
+Options for configuring email notifications or sending peer configurations via email. 
+By default, emails will only be sent to peers that have a valid user record linked. 
+To send emails to all peers that have a valid email-address as user-identifier, set `allow_peer_email` to `true`.
 
 ### `host`
 - **Default:** `127.0.0.1`
@@ -418,6 +421,12 @@ Options for configuring email notifications or sending peer configurations via e
 - **Default:** `false`
 - **Description:** If `true`, emails only contain a link to WireGuard Portal, rather than attaching the full configuration.
 
+### `allow_peer_email`
+- **Default:** `false`
+  - **Description:** If `true`, and a peer has no valid user record linked, but the user-identifier of the peer is a valid email address, emails will be sent to that email address.
+    If false, and the peer has no valid user record linked, emails will not be sent.
+    If a peer has linked a valid user, the email address is always taken from the user record.
+
 ---
 
 ## Auth
diff --git a/internal/app/mail/manager.go b/internal/app/mail/manager.go
index 7b9b3b9..21f50f3 100644
--- a/internal/app/mail/manager.go
+++ b/internal/app/mail/manager.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"log/slog"
+	"net/mail"
 
 	"github.com/h44z/wg-portal/internal/config"
 	"github.com/h44z/wg-portal/internal/domain"
@@ -101,29 +102,15 @@ func (m Manager) SendPeerEmail(ctx context.Context, linkOnly bool, style string,
 		}
 
 		if peer.UserIdentifier == "" {
-			slog.Debug("skipping peer email",
-				"peer", peerId,
-				"reason", "no user linked")
-			continue
+			return fmt.Errorf("peer %s has no user linked, no email is sent", peerId)
 		}
 
-		user, err := m.users.GetUser(ctx, peer.UserIdentifier)
-		if err != nil {
-			slog.Debug("skipping peer email",
-				"peer", peerId,
-				"reason", "unable to fetch user",
-				"error", err)
-			continue
+		email, user := m.resolveEmail(ctx, peer)
+		if email == "" {
+			return fmt.Errorf("peer %s has no valid email address, no email is sent", peerId)
 		}
 
-		if user.Email == "" {
-			slog.Debug("skipping peer email",
-				"peer", peerId,
-				"reason", "user has no mail address")
-			continue
-		}
-
-		err = m.sendPeerEmail(ctx, linkOnly, style, user, peer)
+		err = m.sendPeerEmail(ctx, linkOnly, style, &user, peer)
 		if err != nil {
 			return fmt.Errorf("failed to send peer email for %s: %w", peerId, err)
 		}
@@ -194,3 +181,37 @@ func (m Manager) sendPeerEmail(
 
 	return nil
 }
+
+func (m Manager) resolveEmail(ctx context.Context, peer *domain.Peer) (string, domain.User) {
+	user, err := m.users.GetUser(ctx, peer.UserIdentifier)
+	if err != nil {
+		if m.cfg.Mail.AllowPeerEmail {
+			_, err := mail.ParseAddress(string(peer.UserIdentifier)) // test if the user identifier is a valid email address
+			if err == nil {
+				slog.Debug("peer email: using user-identifier as email",
+					"peer", peer.Identifier, "email", peer.UserIdentifier)
+				return string(peer.UserIdentifier), domain.User{}
+			} else {
+				slog.Debug("peer email: skipping peer email",
+					"peer", peer.Identifier,
+					"reason", "peer has no user linked and user-identifier is not a valid email address")
+				return "", domain.User{}
+			}
+		} else {
+			slog.Debug("peer email: skipping peer email",
+				"peer", peer.Identifier,
+				"reason", "user has no user linked")
+			return "", domain.User{}
+		}
+	}
+
+	if user.Email == "" {
+		slog.Debug("peer email: skipping peer email",
+			"peer", peer.Identifier,
+			"reason", "user has no mail address")
+		return "", domain.User{}
+	}
+
+	slog.Debug("peer email: using user email", "peer", peer.Identifier, "email", user.Email)
+	return user.Email, *user
+}
diff --git a/internal/config/mail.go b/internal/config/mail.go
index 9cc2b5b..56df2b0 100644
--- a/internal/config/mail.go
+++ b/internal/config/mail.go
@@ -41,4 +41,6 @@ type MailConfig struct {
 	From string `yaml:"from"`
 	// LinkOnly specifies whether emails should only contain a link to WireGuard Portal or attach the full configuration
 	LinkOnly bool `yaml:"link_only"`
+	// AllowPeerEmail specifies whether emails should be sent to peers which have no valid user account linked, but an email address is set as "user".
+	AllowPeerEmail bool `yaml:"allow_peer_email"`
 }