iCloud: Write and send email
You can send and reply to messages that you receive using Mail on iCloud.com.
Click the Compose button.
Type one or more names or email addresses in the address field. Press Return or type a comma to end each name or address.
As you type, iCloud Mail tries to suggest a complete address. To use it, press Return.
If a list of suggested addresses appears, click one to use it.
To view all of your contacts, click the Add button at the right end of the address field.
To include Cc and Bcc address fields, click Cc/Bcc.
In the Subject field, type a subject for the email.
If you want to send the message from an address you don’t usually use, click From, then choose a different address from the pop-up menu.
You have multiple addresses if you created an email alias or you have an @me.com or @mac.com address in addition to your @icloud.com address.
Type your message, then click Send in the upper-right corner of the iCloud Mail window.
Note: If you send an email with large attachments, it might be returned by the recipient’s email service because your email exceeds the size limit set by that email service. You can try sending the contents of your message in multiple emails, or using compression software, such as the Compress feature on a Mac, to make your attachments as small as possible.