It depends on settigns at your, and the recipient's, email server. Typical settings are 5MB, 10MB or 20MB.
If your email server allows 20MB attachments but the recipient's server only allows 10MB attachments then the lower limit applies. You'd be able to send a message with a 15MB file attached but the recipent's server won't accept it so the message will bounce back.
Sending files bigger than 5MB by email is usually not a good idea (it may fail, it takes a long time, it clogs the email systems slowing other people's mail down, it wastes storage space on the sender's and recipient's mail server) and you should seek an alternative method.
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