iCloud: If you have trouble sending email
If you get an error when you try to send email
If you recently changed your iCloud account password, and you use an email application to send iCloud email (instead of using a browser), make sure to update your account information in the email application. Also, if you use the Mail app on a Mac, choose Apple menu > System Preferences, click iCloud, and type your new password.
If you use an email application to send your iCloud email, make sure the application’s SMTP (outgoing) server is smtp.mail.me.com or an address provided by your Internet service provider (ISP). To find out your ISP’s SMTP server address, read the information you received when you signed up for your account, visit your ISP’s website or call its support line, or look at the settings for another email account that uses your ISP’s server.
If you use smtp.me.com for your SMTP server, make sure you turn on SMTP authentication in your email program using your iCloud account name and password, and make sure the email address in the From field of your email message matches your iCloud account name. If the trouble continues, have your email program use your ISP’s SMTP server instead.