Graduate students, faculty, and staff are provided with Exchange Online accounts for email, calendar services, task lists and digital voicemail. Undergraduates are provided with Google Apps @ Illinois accounts for email, calendar services, online document collaboration, file storage and chat.
Faculty, staff, and graduate students can access their email by logging in to Exchange Online (using Office 365 if you have been migrated).
Otherwise if you have not been migrated yet you can use https://webmail.illinois.edu/.