Retrieval of all users in Exchange online

Question

Exchange Version: Exchange Online at Office 365
API Name: EWS API 2.0
IDE: Visual basic C# 2010
Targeted features: Impersonation and retrieval of all users
Hi there, I am currently developing a program that uses impersonation and queries the EWS API to retrieve emails and their attachments from users. I have used the C# codes from the MSDN Library to develop the program. The program is successful in retrieving
the emails from specific users that are hard coded into the program.
The code below shows the process of authenticating the admin user and the impersonation is done in the  RetrieveEmailFromUser() function.
ServicePointManager.ServerCertificateValidationCallback = CertificateValidationCallBack;
ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2013_SP1);
service.Credentials = new NetworkCredential("adminemail@", "password", "domain.onmicrosoft.com");
service.AutodiscoverUrl("adminemail", RedirectionUrlValidationCallback);
List<string> emailaddrlist = new List<string>();
emailaddrlist.Add("[email protected]");
emailaddrlist.Add("[email protected]");
foreach (string item in emailaddrlist)
string content = RetrieveEmailFromUser(service, item);
Console.WriteLine(content);
        static string RetrieveEmailFromUser(ExchangeService service, string emailAddr)
            service.ImpersonatedUserId = new ImpersonatedUserId(ConnectingIdType.SmtpAddress, emailAddr);
            FindItemsResults<Item> findResults = service.FindItems(WellKnownFolderName.Inbox, new ItemView(50));
As can be seen from the coding, the users that are to be impersonated have been hardcoded. I would like to know if there are any C# codes or a link to a page where it describes how I can retrieve ALL users with mailboxes from a Microsoft 365 admin account
without needing to manually add users for retrieval.

Answer 1

Hi there sorry for asking again but I have successfully retrieved all the users but now I would need to filter them to lower the amount of addresses retrieved.
For example
owershell.Runspace = runspace;
//Create the command and add the parameters to retrieve all users that have mailboxes
powershell.AddCommand("Get-Mailbox");
powershell.AddParameter("RecipientTypeDetails", "UserMailbox");
//Invoke the command and store the results in a PSObject collection
Collection<PSObject> EmailList = powershell.Invoke();
//Iterate through the results and add the PrimarySMTP address for each mailbox to emailAddrlist
foreach (PSObject emailAddr in EmailList)
string time = emailAddr.Properties["WhenCreated"].Value.ToString();
string addr = emailAddr.Properties["PrimarySmtpAddress"].Value.ToString();
EmailAddrList.Add(addr + time);
The property ("WhenChanged") will retrieve the date time when the mailbox had its options MODIFIED but not when an email is received. Is there a parameter I can input using powershell to retrieve users who have new emails in their mailboxes from
a specific? Or can I change the value of the Property from  ("WhenChanged") to something else that will give me a date time of the most recent addition of an email to the mailbox. This will then allow me to compare the date time to filter out
addresses which have not received any emails.
Thank you.