not work for the WordPress5.6.1

I use easy wp smtp plugin to send email, and I send the test email to my other email address is normally received, but the Subscribe to Download plugin not work, I create the form and test subscribe , when I input the email address and click the subscribe&download button and the form warning the email is send successfully, everything looks normally , but nothing to do , I have no received the email and the admin subsciber panel has no subscriber , so what should I do