For Saltcorn to send email, an SMTP server needs to be configured. If you have a Gmail account, you can use the Gmail SMTP server. There are limits on the amount of emails you can send, but if you run a small site it may be sufficient. The limit varies, but currently appears to be 500 emails per day for free gmail accounts.
First, you must obtain an application specific password to your Gmail account.
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.