User2 must be able to view reports and schedule the email delivery of security and compliance reports.
The Security Reader role can view reports.
The Compliance Management role can schedule the email delivery of security and compliance reports.
Reference:
https://docs.microsoft.com/en-us/exchange/permissions-exo/permissions-exo
Topic 1, Contoso, Ltd
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Overview
Contoso, Ltd. is a consulting company that has a main office in Montreal and two branch offices in Seattle and New York.
The offices have the users and devices shown in the following table.

Contoso recently purchased a Microsoft 365 E5 subscription.
Existing Environment
The network contains an Active directory forest named contoso.com and a Microsoft Azure Active Directory (Azure AD) tenant named contoso.onmicrosoft.com.
You recently configured the forest to sync to the Azure AD tenant.
You add and then verify adatum.com as an additional domain name.
All servers run Windows Server 2016.
All desktop computers and laptops run Windows 10 Enterprise and are joined to contoso.com.
All the mobile devices in the Montreal and Seattle offices run Android. All the mobile devices in the New York office run iOS.
Contoso has the users shown in the following table.

Contoso has the groups shown in the following table.

Microsoft Office 365 licenses are assigned only to Group2.
The network also contains external users from a vendor company who have Microsoft accounts that use a suffix of @outlook.com.
Requirements
Planned Changes
Contoso plans to provide email addresses for all the users in the following domains:
East.adatum.com
Contoso.adatum.com
Humongousinsurance.com
Technical Requirements
Contoso identifies the following technical requirements:
All new users must be assigned Office 365 licenses automatically.
The principle of least privilege must be used whenever possible.
Security Requirements
Contoso identifies the following security requirements:
User2 must be able to view reports and schedule the email delivery of security and compliance reports.
The members of Group1 must be required to answer a security question before changing their password.
User3 must be able to manage Office 365 connectors.
User4 must be able to reset User3 password.

You can invite guest users to the directory, to a group, or to an application. After you invite a user through any of these methods, the invited user's account is added to Azure Active Directory (Azure AD), with a user type of Guest. The guest user must then redeem their invitation to access resources. An invitation of a user does not expire.
The invitation will include a link to create a Microsoft account. The user can then authenticate using their Microsoft account. In this question, the vendors already have Microsoft accounts so they can authenticate using them.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/b2b/add-users-administrator

Reference:
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-pta-quick-start