I noticed that the event send is deprecated, so I was wondering what is the approach we should be taking? For now I am using integration-send-receiver function, but I am not sure if that is the correct approach.
You are doing the right thing. The use of SysMail has been deprecated in favour of using a mail integration channel. You create a mail channel and configure it in your environment connections settings. Then send mail messages (message (: :class "Mail") (: ...) over the channel either by using an integration service, or as you mentioned the (integration-send-receive ...) function.