It's important that make sure that all email with an @letu.edu address in the FROM: field is legitimate and authorized.
SPF allows LETU to let outside mail servers know which mail servers are authorized to send mail on behalf of our domain. LETU publishes a SPF record in DNS that lists our LETU mail servers and mail servers authorized to send on our behalf. When an outside mail server receives mail, it can look at our SPF record and see if the mail server it received the mail from is in the list. If it's not in the list, that mail server may or may not accept delivery of the mail.
DKIM makes use of cyptographic authentication in an attempt to make sure the sender of an email is authorized to send from a domain. LETU publishes a public DKIM key in our DNS, and signs all outbound email. Mail servers that receive mail from @letu.edu senders perform a DKIM check against the DKIM key in our DNS and take action based on whether the email passes the DKIM check or not.
DMARC allows us to tell other mail servers how they should treat email from us when they receive it. This means that once we have SPF and DKIM configured properly, we can instruct any outside mail servers to reject email that fails SPF/DKIM checks and claims to be from us. Another useful part of DKIM is that we receive reports from other mail servers of the mail claiming to come from @letu.edu. This allows us to monitor any person or company attempting to send email on our behalf for compliance with our email security procedures.