This is an old revision of the document!
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 at extra cost.
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