I’ve done some tests with the Email Alerter and here is what I found.
I assume you use a Gmail account with that element. Recently, Google added new security features that restrict using Gmail accounts in third-party applications. In particular, you can not use your main password in such connections. Instead, you need to enter a specially generated “application” password. You can create it by following this instruction Note that you need the 2-step verification enabled on your account.
Once you have the application password, enter it in to the “Sender Password” on the Alerter element. Other properties can stay as before but check that ‘Enable SSL’ is true and SMTP port is 587. Now, the emails should be sent as before.
Another solution would be using an SMTP mail server of your institute and reconfigure all Alerter elements to use it. Your technical support team should give you settings for SMTP.