If you're joining Wednesday's Day Without A Woman protest–or striking with in solidarity with people around the world for the International Women's Strike–organizers already have you covered with the perfect out-of-office auto email response.
[Your personal greeting]
Thank you for your email. I’m out of the office today to participate in the Women’s March on Washington’s Day Without A Woman in observance of International Women’s Day. I am not working today and will respond to your message tomorrow. For anything urgent, please contact [Insert name of male colleague covering your work, if applicable].
[Insert your name]
They've already done half the work for you! Now you just need to do the other half–finding events in your area if you're joining the strike, or seeking out other avenues to participate if you're not able to strike.