Many Internet Service Provider dynamically-assigned IP addresses are appearing on block lists more frequently. As a Purdue-affiliated user, you do have the option of configuring your e-mail client, so that e-mail sent to @purdue.edu e-mail addresses is not quarantined. This is done through the use of SMTP Authentication.
Information on how to configure many commonly used e-mail clients can be found on the webpage:
Mailhub Client Setup