Newly created users wont send to internal exchange

First off, please excuse my ignorance. My MSP has brought on a new customer who is setup using cpanel for dns. It also seems to be setup for external email transfer as well. All email seems to be flowing fine except for newly created users. Here is what I have done: 1) created new email account on cpanel 2) go on customer's internal exchange 2019 server and create their email account/active directory account 3) I wait an hour and try sending a test email, from my email account, to the newly created address. It seems any external email is not going to the new user's exchange inbox. However, it is working for existing users and I have gone through every setting and even ad attributes and I cannot find what might be missing. Again, excuse my ignorance. I am not used to this platform and I have not touched a dedicated exchange server in years as ive basically lived in the office 365 world for years now.