shared account vs regular account in 365

Depends on the APIs in use. Generally speaking, you're not supposed to be using the shared mailbox credentials directly, but impersonation will work fine.

does shared mailbox have credentials at all?

Hi,

When you are referring to a shared mailbox does it have a license assigned, in this case, it will have credentials to access. If the mailbox is truly a shared-mailbox type then it will be permissions assigned to who will access the mailbox and will not have a credential.

-Arun

Every shared mailbox has a matching user object, you can easily confirm this within the Users section of the M365 Admin center. However, the credentials for said user are managed by the service. Technically, you can reset the password and use it to login directly, however this is in violation of the license agreement. Thus, you need to rely on impersonation for API access.

A shared mailbox in Microsoft 365 does not have or require a license.  If you remove a license from a user account, the mailbox will be deleted after 30 days.  This is not the case with a shared mailbox.

I'm talking about a true shared mailbox...

I guess thats my point.  For SHARED mailbox, there really isn't a way to tie into other systems unless you have a login account which a shared account doesn't have.  Thanks.