diff --git a/intelmq/bots/outputs/smtp_batch/output.py b/intelmq/bots/outputs/smtp_batch/output.py
index 66568f259..f1277af18 100644
--- a/intelmq/bots/outputs/smtp_batch/output.py
+++ b/intelmq/bots/outputs/smtp_batch/output.py
@@ -238,7 +238,7 @@ def prepare_mails(self):
                         continue
                 else:
                     # visible both warning and print
-                    self.logger.warning(f"Warning: %s timeout, too big to read from redis", mail_record)
+                    self.logger.warning("Warning: timeout, too big to read from redis: %r", mail_record)
                     self.timeout.append(mail_record)
                     continue
 
@@ -256,7 +256,7 @@ def prepare_mails(self):
                     if threshold and row["time.observation"][:19] < threshold.isoformat()[:19]:
                         continue
                 except KeyError:
-                    self.logger.warning(f"Warning: %s row skipped due to time.observation error", mail_record)
+                    self.logger.warning("Warning: row skipped due to time.observation error: %r", mail_record)
                 fieldnames = fieldnames | set(row.keys())
                 keys = set(self.allowed_fieldnames).intersection(row)
                 ordered_keys = []
@@ -292,7 +292,7 @@ def prepare_mails(self):
                     try:
                         zf.writestr(filename + ".csv", output.getvalue())
                     except Exception:
-                        self.logger.error(f"Cannot zip mail %s", mail_record)
+                        self.logger.error("Error: Cannot zip mail: %r", mail_record)
                         continue
 
                 if email_to in self.alternative_mail: