Standard e-mail is Synology Mail Server app.
https://kb.synology.com/en-global/DSM/help/MailServer/mailserver_desc?version=7
Webmail is provided by Mail Station app (RoundCube).
Advanced e-mail is available with Synology MailPlus app. 5 users are free and more are at extra cost.
Mobile apps are available.
Outlook uses IMAP.
https://www.synology.com/en-global/products/MailPlus_License
https://kb.synology.com/en-global/DSM/tutorial/Quick_Start_MailPlus_admin
https://kb.synology.com/en-global/DSM/tutorial/Quick_Start_MailPlus_users
https://kb.synology.com/en-us/DSM/tutorial/How_to_access_files_on_Synology_NAS_via_FTP
https://kb.synology.com/en-global/DSM/help/DSM/AdminCenter/file_ftp_setting?version=7