Sending email to the Team Site's email address is not working

we are using sharepoint online "Office 365 Enterprise E3" plan. and i want to do the following:-

1. Create a public office 365 group which contain some users.

2. Give the public office 365 group email address = HRManagers@ourcompany.com.so when users send an email to this email address, all the group's members users should receive it.

so i follow those steps:-

1. inside the sharepoint admin site >>click on + Create >> Team site, as follow:-

2. i entered the following inside the group name and email:-

3. i entered the group admins and members. then a new team site was created. and when i hover over the site title i got this email addressHRManagers@ourcompany.onmicrosoft.com

4. i tried to send an email to this email address HRManagers@ourcompany.onmicrosoft.combut i got delivery failure that the email address can not be found.

5. So i waited for around 3 hours i check the site again. and i hover over the site title. but i have noted that the email address was changed fromHRManagers@ourcompany.onmicrosoft.com toHRManagers@ourcompany.com.

so i tried to send another email to HRManagers@ourcompany.combut i got this delivery failure email:-

#550 5.1.1 RESOLVER.ADR.RecipNotFound; not found ##

1. Why i am unable to send emails to the team site's email address either HRManagers@ourcompany.onmicrosoft.com ORHRManagers@ourcompany.com.

2. Why the team site's email address got automatically changed from HRManagers@ourcompany.onmicrosoft.com toHRManagers@ourcompany.com. ?? although i need the updated email address, but not sure how it got changed? now inside our Domain list we have the following 2 domains:-

so can anyone advice on my above 2 questions please?

Thanks