If you are setting email alerts and getting troubled with what should be input in SMTP Server and Port, this article will be helpful for you.

Applies to: All Reolink Cameras and NVRs.

The SMTP Server and Port vary depending on the mailbox that you are using. If you set Gmail as the Sender Address, you may leave the default SMTP Server (smtp.gmail.com) and default Port (465 when SSL or TLS is enabled and 25 when SSL or TLS is disabled) unchanged. However, if you set another mailbox, such as Hotmail, or Yahoo mail, as Sender addresses, you will need to input the corresponding SMTP server & SMTP port for the e-mail test.

Here for your reference: