Under certain circumstances in Gmail, G Suite for Domains (formerly known as Google Apps), and Office 365, mail is de-duplicated, resulting in you receiving only one copy of a message sent to you multiple times, or you not receiving messages sent via uchicago.edu to your Google accounts.
If you forward your uchicago.edu mail to a Gmail (https://mail.gmail.com) or UChicago G Suite for Domains example.com address and then try to send a message from Gmail or UChicago G Suite to your uchicago.edu address, you will never receive it in your Gmail/G Suite inbox. This is because of Google's message de-duplication.
This also happens if you send to @lists.uchicago.edu address from Gmail/G Suite for Domains. If you are a subscriber to the @lists.uchicago.edu address, you will never receive the message as distributed by the lists.uchicago.edu server.
Example One:
Bob@gmail.com is a subscriber to fakelist1@lists.uchicago.edu. Bob sends a message to fakelist1@lists.uchicago.edu. Bob will never see the distributed message from fakelist1@lists.uchicago.edu in the Gmail inbox.
Example Two:
Bob@uchicago.edu forwards his mail to his private Gmail account, bob@gmail.com. Bob sends a message from Gmail to his uchicago.edu account, bob@uchicago.edu, to test if mail forwarding works. Bob will never see the message in the Gmail inbox.
If you are a subscriber of two @lists.uchicago.edu addresses and a single message is sent to both lists, your Office 365 account will receive one copy only of the distributed message.
Example:
Bob, an Office 365 user, is a subscriber for fakelist1@lists.uchicago.edu and fakelist2@lists.uchicago.edu. Sally sends a message To: fakelist1@lists.uchicago.edu and Cc: fakelist2@lists.uchicago.edu. Bob will receive this message once, and it may appear to come from either fakelist1@lists.uchicago.edu or fakelist2@lists.uchicago.edu.