If you’re on strike you could leave a message something like this:
“Thanks for you email.
I will not be working again until Thursday 3rd March because I’ll be taking strike action as part of UNISON’s campaign for decent pay. The 1.5% increase which was imposed on us in August 2021, following the previous year’s pay freeze, means that our wages are worth significantly less than they were, and with the increases to the cost of living, we can’t afford to accept real terms pay cuts.
If you’re a UNISON member, please join me in taking strike action which UNISON members voted for. If you’re not in a trade union, I suggest you join one and join our campaign for decent pay.”
If you’re feeling brave, you could say that all emails received on 1st and 2nd March will not be answered and will need to be re-sent.
The point of striking is to not work for the strike days, so please don’t try to catch up with the lost work afterwards. You need to make some judgement on what’s reasonable, but we all do that anyway, don’t we?