The maximum size of email attachments is 10 MB on our older DirectAdmin\Helm hosting plans.
On our cp.blacknight.com hosting plans this limit is 30MB.
altmail.blacknight.com can handle up to an 8mb attachment
We do NOT recommend using email to transfer large files. Use FTP or services like DropBox - they're more efficient and less likely to cause issues for people who check email on their mobile devices