how to send 1 email to all contacts

Not sure but the app Speed Names allows you to create groups and address and email to an entire group. You may be able to use this to create a group containing all your contacts and address the email to the entire group at once.

Hi Friend,

You do not need to download any app...

In your PC, open your iCloud from website. In contacts, click in the Red icon. It will open your contact groups. There have your All contact Group. If you click in "+" icon, you can create your own contact groups.

To add your contacts in the new Group List, you open your All Contact Group, click and hold a contact and drag to the New Group Contact...

In your device, open your contacts app and update them tapping the update buttom. Groups will appear.

Now, open your email in your device, write down the Group Name you want to send the email and, voala... Just works.

Hope it will be helpfull.

Man you wasted more time writing on this forum you needed to test your solution... You would have seen you can't select a group as email recipient. Natively.