[Urgent]: The Most Important Thing You’ll Learn About Email Subject Lines Today
blog.sanebox.com/2016/04/04/email-subject-line-abbreviations-eom
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
Ten subject line abbreviations and phrases that will make email work for you. Include them to increase clarity and avoid unnecessary email exchanges, thereby improving life for you and for everyone you email.