diff --git a/internal/user/sync.go b/internal/user/sync.go
index 87ba6ca1..677d0ffc 100644
--- a/internal/user/sync.go
+++ b/internal/user/sync.go
@@ -513,7 +513,16 @@ func (user *User) syncMessages(
 				result, err := parallel.MapContext(ctx, maxMessagesInParallel, chunk, func(ctx context.Context, msg proton.FullMessage) (*buildRes, error) {
 					defer async.HandlePanic(user.panicHandler)
 
-					return buildRFC822(apiLabels, msg, addrKRs[msg.AddressID], new(bytes.Buffer)), nil
+					kr, ok := addrKRs[msg.AddressID]
+					if !ok {
+						return &buildRes{
+							messageID: msg.ID,
+							addressID: msg.AddressID,
+							err:       fmt.Errorf("address does not have an unlocked keyring"),
+						}, nil
+					}
+
+					return buildRFC822(apiLabels, msg, kr, new(bytes.Buffer)), nil
 				})
 				if err != nil {
 					return