Think twice about sending attachments and images. You can always let people know what you have and then send them out to those who request them. Few people like large downloads of information that they won't use. Do not send executable files or files with macros as they may contain viruses. Mailgroup members are advised to immediately delete such files.
Executable files are ususally programs.
Subject headings . are used by many to decide if they are going to read the Email. Make sure they remain relevant. If you don't want the mail to build up while you are away then consider unsubscribing and then rejoining when you get back. This is particularly important for those who have limits on the size of their Mailboxes on the ISP's server. Mail sorting .