NOTE: If ever the format of message ids is changed, the regular expression for
checking that a string is in this format must be updated in a corresponding
way. It appears in the initializing code in exim.c. The macro MESSAGE_ID_LENGTH
-must also be changed to reflect the correct string length. Then, of course,
-other programs that rely on the message id format will need updating too. */
+must also be changed to reflect the correct string length. The queue-sort code
+needs to know the layout. Then, of course, other programs that rely on the
+message id format will need updating too. */
Ustrncpy(message_id, string_base62((long int)(message_id_tv.tv_sec)), 6);
message_id[6] = '-';