Just remember that email is primarily a messaging system not a file transfer system and thus has message size limitations.
I think the default setup is 8Mb for most mail transfer agents (MTA).
As stated above, all your attachments are encoded and become part of the message. If your message is too big then most MTAs will drop it and get on with processing other messages.
Then there is the issue from the recipients point of view of exceeding their personal mailbox quota by receiving an email with a huge attachment.