- /* As part of the new metadata record, measure how
- * big this message will be when displayed as RFC822.
- * Both POP and IMAP use this, and it's best to just take the hit now
- * instead of having to potentially measure thousands of messages when
- * a mailbox is opened later.
+ /*
+ * Measure how big this message will be when rendered as RFC822.
+ * We do this for two reasons:
+ * 1. We need the RFC822 length for the new metadata record, so the
+ * POP and IMAP services don't have to calculate message lengths
+ * while the user is waiting (multiplied by potentially hundreds
+ * or thousands of messages).
+ * 2. If journaling is enabled, we will need an RFC822 version of the
+ * message to attach to the journalized copy.