The only time that an email template with an attachment will not send out is if you have:
Any file that gets uploaded into the file repository has a unique URL address that the system picks up to attach it to the email each time you send out the email template with the file attachment.
If you move, update or remove the file then the attachment breaks and the email will not send out.
To ensure emails with attachments get sent - any changes you make to a file attachment - you need to remove the original file attachment from the email template and replace it with the new one.
2. The email will not be sent out if the file attahment(s) exceeds 7 MB in file size. The email platform limits the maximum size of an attachment to 7MB so please bear this in mind when using attachments to an email that is sent out via the internal pop up email platform.