In DFP (file manipulation > file upload) there is a box to tick for web Images Only. If you do choose Web Images Only, on the next page of the wizard, you can resize the image if you wish.
What I'm asking is, is that functionality available from within the Create Email Message > Manage Email Attachment area of UE4. It doesn't seem to be in the wizard but is it available after the behaviour has been applied. I'm particularly interested in restricting the maximum file size of an attachment to an email.
If it isn't then fine, but if it is then how would I go about it.