Zoho Mail Message and Attachment Size Limits
Zoho Mail allows attachment files with a size up to 20 MB, with a limit of 20 MB per email message if you add several attachments. However, if you are using Zoho Mail through an organization, your mail administrator can set a different limit. To send larger files, you can try a file sending service instead of attaching the documents directly.
554 Mail Error for Oversized Messages
If somebody tries to send you an email exceeding the size limits, they will receive a “Delivery Status Notification (Failure)” message that gives as the reason for the failure to deliver. This is often called the bounce message. This is an SMTP error message. Error codes beginning with 554 are returned from the server after you attempt to send the message. The message bounces back to you undelivered, and you get this often-cryptic code and vague message. The 554 error is catch-all code for email delivery failure. You will see it often if your emails bounce back undelivered for many reasons. The 5.2.3 after the 554 gives a little more information. The 5 means that the server has encountered an error and this is a permanent failure for the delivery of the message. The second number, 2, means the mailbox connection status was the reason. If it is a 5.2.3, this means the message length exceeds administrative limits. Other familiar 554 codes are:
554 5.1.X: Used for bad destination addresses.554 5.2.1: Mailbox disabled, not accepting messages.554 5.2.2: Mailbox full.554 5.3.X: Used for mail system status errors.
The full list of Enhanced Mail System Status Codes can be viewed in detail if you want to decode more of them.
