This is exactly Termux's point, to subvert Android into linux cheaply. Same for MinGW or MSYS2. I want to invest as few as possible on Andriod or Windows, while still able to use them in the way that I prefer.
SPAM filters are useless anyway. I only filter the shit that don't even adhere to proper SMTP protocol and let everything in. I just mentally ignore SPAM in my inbox.
Simple filters in free software don't do much unless you spend your energy tweaking it, sophisticated filter like Gmail's has a hidden agenda against you.