Is there an attachment file size limitation?
Yes, there is a limit. The total size of a sent message, including text and all attachments, cannot exceed 50 megabytes when using a mail client such as Thunderbird or Outlook. Users of the Enhanced layout mode of Webmail should also be aware that the auto-save function in that mode temporarily stores drafts of outgoing messages in your Drafts folder so your disk quota must have at least two times the size of the message and attachment.