Initially, Zabbix has several predefined notification delivery methods (media types). Email is one of those. Email configuration can be found under Menu → Administration → Media types.
Click on Email in the list of pre-defined media types.
Set correct SMTP server, SMTP helo and SMTP email values. Press Save when ready.
SMTP email is used as the From address for outgoing e-mails.
Now you have media type "Email" defined. A media type must be linked with users, otherwise it will not be used.