The Windows ISO file is too large – Boot Camp Assistant creates a [X] GB installer partition which will contain the files present on the Windows 10 ISO as well as the Boot Camp Support software.

This message appears when a picture, video, or any other file attached to a message is too large to be sent over text.

If your OST file is too large, then to reduce the size of the Outlook OST file, you can use the working solutions laid down in this post.