We were unable to reproduce the issue that you reported. We used the code snippet given below for testing.
ImapClient imapClient = new ImapClient();
imapClient.Host = "imap-mail.outlook.com";
imapClient.Port = 993;
imapClient.Username = "Email";
imapClient.Password = "Password";
imapClient.SupportedEncryption = EncryptionProtocols.Tls12;
imapClient.SecurityOptions = SecurityOptions.SSLImplicit;
ImapMessageInfoCollection msgsColl = imapClient.ListMessages();
Console.WriteLine("Total Messages: " + msgsColl.Count);
ImapFolderInfoCollection folderColl = imapClient.ListFolders();
Console.WriteLine("Total Folders: " + folderColl.Count);
We hope that this fixed the issue that you were facing. Please feel free to reach us if further assistance is required.