It's very important that any email communication is not unsolicited. We recommend only contacting professors if you have a pre-existing and genuine relationship with the person.
This can be a very positive exercise if managed carefully. If a professor is interested in using your film in class, or assigning it to his/her students to watch, they are grateful for the relevant marketing messages.
On the other hand, if the professor considers your email as sales spam, they may consider it unsolicited and take further action.
If you are marketing to professors who have your film on PDA, it is important to acknowledge that videos have been brought to them by their library and are being paid for out of the library budget. Most professors know this, but it's still good to remind them that the hard-working librarians are bring them all these great films!