I work in IT and probably know better than you. What systems would you go to for past communication? The phone company? Do you really think they record your conversations? They don't. I worked for a national phone company in IT for 2 years and know the systems intimately. When people talk about "metadata" do you know what it means? I do, because I wrote code to deal with that data.
Do you think your email provider keeps your email? They may, if you configure your email to be saved after you read it (meaning it was copied to your PC). Even so they limit how much they'll keep. Most people delete it from the provider as it is copied to your system.
My provider keeps my deleted email for 3 days.
Tweets may be saved longer. I'm less familiar with that system, but it does seem like it is searchable. Any evidence that Page was tweeting with the campaign?