This problem has been solved in version 8.0.3. In order to send emails with correct structure and fixing this problem, you need to use SMTP Connections configured in the app.
By default, JETI sends html email with mime type multipart/related. This is interpreted and handled correctly by the vast majority of email clients including Outlook, Thunderbird, Gmail, Yahoo, and a lot others but Mail app on iOS.
Mail app on iOS devices does not show attachments from emails with mime type multipart/related. The solution is to configure JETI to change the mime type of the emails to multipart/mixed.
In order to enable multipart/mixed, open the Configuration tab of the JETI admin screen and enable the option as shown below.
Problems with Thunderbird
One problem we have found was that multipart/mixed emails cause problems in Mozilla Thunderbird. So be careful with enabling this option in JETI.
See JETI-504 for more details.