Below is an example implementation:

import "server-cli-only"
 
import {
  USE_DEVELOPMENT_SEND_PLUGIN,
  notImplemented,
  type OberonPlugin,
} from "@oberoncms/core"
 
const EMAIL_FROM = process.env.EMAIL_FROM
const SEND_SECRET = process.env.SEND_SECRET
 
export const sendPlugin: OberonPlugin = () => ({
  name: "Custom Send",
  disabled: USE_DEVELOPMENT_SEND_PLUGIN,
  adapter: {
    sendVerificationRequest: async ({
      email,
      token,
      url,
    }: {
      email: string
      token: string
      url: string
    }) => {
      const msg = {
        from: EMAIL_FROM,
        to: email,
        subject: "One time login to Oberon CMS",
        text: `Sign in with code\n\n${token}\n\n ${url} \n\n`,
      }
 
      if (!SEND_SECRET) {
        throw new Error("No SEND_SECRET configured")
      }
 
      // Replace this with your own send function
      await sendEmail(msg, SEND_SECRET)
    },
  },
})