For Saltcorn to send email, an SMTP server needs to be configured. If you have a Yandex account, you can use the Yandex SMTP server.
There are no limit for amount of emails that can be send. But there are few limits for recepients of emails. The limit for recepients in one mail over SMTP is 50 recepients. All emails from one email address limits by 3000 recepients per day.All emails from one domains limits by 5000 recepients per day. More information about limits https://yandex.ru/support/connect/mail-limits.html.
Then fill in the email settings in Saltcorn (Settings menu, About application -> Email) with the following values:
Click Save to save the settings. You can now enable settings that require an email server, for instance password reset or use the send email action.
On more recent versions of Saltcorn, you can click the "Send test email" button below Save to check that your email configuration works. This will send an email to your email-from-address if correctly configured.