I remember from N9 forum a simple trick with email attachments. You need yo edit one file, just write 50 instead 25, to have change size of attachments. Is that possible in SF? 25MB holds 6-7 photos or few seconds of video. Modern servers have 100MB, so let users to decide.
Do you mean the maximum Attachment size that will be downloaded?
Or maximum size of attachments that can be attached to an email when writing it new on the device?
While sending. In mail creator, if you atach files bigger than 25MB, it’s appear red warning and email can’t be sent.