+# %m / %{msgid} - Message-ID
+# %s / %{subject} - Subject
+# %f / %{from} - From address
+# %p / %{size} - Physical size
+# %w / %{vsize} - Virtual size
+# %e / %{from_envelope} - MAIL FROM envelope
+# %{to_envelope} - RCPT TO envelope
+# %{delivery_time} - How many milliseconds it took to deliver the mail
+# %{session_time} - How long LMTP session took, not including delivery_time
+# %{storage_id} - Backend-specific ID for mail, e.g. Maildir filename