diff --git a/domain/mail-repository.js b/domain/mail-repository.js
index 4b8a0c2..149b3f0 100644
--- a/domain/mail-repository.js
+++ b/domain/mail-repository.js
@@ -29,6 +29,8 @@ class MailRepository {
 	add(to, mailSummary) {
 		if (to !== undefined) {
 			this.mailSummaries.set(to.toLowerCase(), mailSummary)
+		} else {
+			debug('IMAP reported no recipient for mail, ignoring', mailSummary)
 		}
 	}