With electronic communications, however, re has been repurposed. RE: in an email subject line precedes the subject when the message is a reply to a previous one that uses the same subject. This indicator helps you and your correspondents recognize messages and responses that are on a particular topic, which is helpful if you’re engaged in several email conversations at the same time.
When RE: Causes Confusion in Emails
RE: is typically added in front of the subject of a reply email automatically. However, if you put it there manually in a new message, meaning to indicate “regarding,” recipients may be confused. They may think the message is a reply that belongs to an email thread they haven’t seen. Regardless of what might be true in other contexts, in email correspondence RE: or Re: doesn’t mean “regarding.” It means “reply.” To prevent confusion, don’t insert RE: in a subject line. The fact of the subject line itself implies that this is what the message is “regarding.” Instead, allow RE: to appear when you reply to an email message sent to you.
