The gmail to notion add-on lets you save email messages from gmail to notion database. You can also, Turn any Notion page into an HTML email and send it to anyone. They also offer a 7 day free trail, where you can check and understand how NotionMail works.
Gmass can show you where your email lands in various Gmail accounts. This is helpful to see what “tab” Gmail is sorting you into, or if you are hitting spam filters.
Using the emails that Gmass provides, send an email to those using Notion Mail. There's no upper limit on how many emails you can send through NotionMail.