What do these mysterious numbers in the subject line of arXiv mailing list emails mean? Every day I receive the latest arXiv abstracts via email, with subject lines such as

physics daily Subj-class mailing a4 1
physics daily Subj-class mailing 124 1
physics daily Subj-class mailing 490 1

With new email clients that create "conversations" from an email chain based on the subject line, the disorderly nature of the subject lines makes it a pain to sift through the last week's abstracts if I haven't kept myself up to date.

What do a4, 124, and 490 mean? These identifiers are not unique to each day's listings, but I cannot spot a correlation between them and the date of the email. Is there some hidden way to either include the date in the subject header, or remove these seemingly random strings?
Straight from the horse's mouth: there is no fix, but an update is on the list of things that "will be done when they're done".


  You may safely ignore the numbers after the text "class mailing" as
  they are used for internal audit code and essentially meaningless from
  a user perspective.
  
  We do have plans to update the mailing code at some stage, but the
  time-line is unclear due to limited developer time.