This article provides the steps moderators can take to customize the Welcome message that goes out to new members and it explains how additional information can be sent via "Auto-send" files. 

A welcome message goes out to all new members when they join your group.  Along with whatever text you compose, Yahoo! Groups provides a default message to members containing information on how to unsubscribe, change message delivery options, etc.

Here’s how to customize a welcome message for your Group:

1. From the list on the left, click Management.
2. Under "Group Settings", click Membership.
3. Click Edit next to "Membership Type and Welcome Message."
4. In the "Welcome" box, compose your message.
5. Click Save Changes.

You can add another message, multiple messages, or a photo to the welcome for new members by uploading a file to the Files section:

1. Click Files from the list on the left of the page.
2. Choose Upon joining group in the "Auto-send to Members" section.

This distributes anything you’d like new members to receive when they join the Group.