If your message is over 100,000 bytes, including attachments, it will be returned to you. I have an attachment that is larger than that. Send it to people directly, not through this list. Or post it on a server for others to download using FTP or a Web browser. Members will then see your message the next time they check their mail.
Some people use it, improperly, to verify routine delivery.
It is a special problem for e-mail lists because of the avalanche of mail it generates. If your message has this header line it will be returned to you, undelivered. Getting On and Off the List 13. I am a department chair. I don't want more e-mail.