Sending your business emails out on a legal holiday, like All Saints’ Day for example, can be a risky move. The chances are that your recipients may not see it until a few days later. By which time your email is probably buried under a pile of email or – even worse! – a mountain of spam (assuming that their inbox is chronologically sorted).
As the more recent messages are likely to receive the most attention, your message may not be as effective as you could have wished. Open rates for emails are strongest within the first two days of delivery. After that, they tend to fall. Like a lead balloon.
On the other hand, an email is the ideal medium to announce that you are taking a day off. E.g. we used our weekly tipmail as an opportunity to inform you that EmailGarage was closed on Thursday 1 and Friday 2 November. See?
Conclusion: send out your email when it’s most likely to get read. This applies to public holidays too.