iCloud: Mailbox size and message sending limits

Mailbox Size

Your iCloud account includes 5 GB of free storage, which is shared by mail, documents, account information, and the iOS settings and app data that are automatically backed up by iCloud. You can also purchase additional storage. 

Limits on Sending Messages   

iCloud has several safeguards to ensure that only iCloud members can send messages using the iCloud outgoing mail server. Among these safeguards are reasonable limitations on:

• The total number of messages you can send each day (200 messages)
• The number of recipients to whom you can send each day (1000 recipients)
• The maximum number of recipients per message (100 recipients)
• The size of incoming and outgoing messages (20 MB)

iCloud email has been designed primarily for personal use. Sending unsolicited bulk email messages through iCloud email servers is prohibited. To review the iCloud membership agreement and acceptable use policy, please see the iCloud Terms and Conditions.

When message sending limits are exceeded, you may see the following alert messages depending on how you view iCloud Mail:

• iOS: "A copy has been placed in your Outbox. Sending the message failed because you exceeded your sending limit."
• OS X: “Cannot send message using the server iCloud.”
• iCloud webmail: "550 5.7.1 membername@icloud.com: You have exceeded your daily sending limit. Please try again later.”

If you continue to exceed message sending limits, try the following methods to resolve the issue:

• Check your Mail Outbox to see if it contains a backlog of messages (messages may be improperly addressed, the destination server may be unresponsive, or the destination account might be over quota).
• Check to see if you have any network monitoring software that might be using your iCloud account to automatically send messages, such as firewalls or internet security software configured to send an alert when a potential security issue is detected.
• If you send messages to groups, make sure all email addresses in the group are valid. (For example, is the recipient's email address spelled correctly or has it changed?)