Correct me if I am wrong, but I will judge that the user knows another telephone email and knows how to add it to the program. The best way, in my opinion, is to either use the task application that the user will need to configure it, or use flashable zip to install the script and run it using crontab.
If you have Busybox in your phone, you can access crontaband sendmail. The idea is to write a small shell script with sendmailand run it on the schedule you want, thanks crontab. This way you can send emails without user confirmation or without having to click or do anything at all.
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