Jun 26, 2019 01:38 PM|mgebhard|LINK
The SMTP server is being set according to the environment.
// The third parameter is useSSL (true if the client should make an SSL-wrapped
// connection to the server; otherwise, false).
await client.ConnectAsync(_emailSettings.MailServer, _emailSettings.MailPort, true);
The community does not know the environment, the the value of _emailSettings.MailServer, and cannot see your appsettings.json files. I assume you need to enable SSL and set the proper SSL port according to your SMPT server.
I recommend setting a break point and single stepping through the code.