I have an email which is used by staff only. We are strictly instructed not to give these out as the fear is that parents will misuse it, sending constant messages or even being directly abusive.
As other teachers have said, we cant reply instantly so its really not appropriate for 'X is away today'. Ringing the office takes 5 minutes max, not much longer than sending an email.
In terms of questions that parents dont have time for at the ends/beginnings of the day then yes it would useful, efficient and proffessional but unfortunately the teacher-parent relationship is more complicated. There's too much opportuniy for misunderstandings when its not face to face. Also, on the more extreme side, if a client sends you abusive message then you cut all contact, cancel any work etc. You can't kick a child out of your class because their Mum's not nice.
There's no point saying that schools should work like the 'real world' (otherwise known as, the office world. So completely forgetting Drs, nurses, bin men, farmers, vets, cleaners, shop assistants and the thousands of other people who dont spend their day sending emails) - school is just not the same.
PSBD - Please stop making out teachers don't understand jobs other than their own. I have had jobs that are not teaching, my DP has a job, my parents had them, my friends have them. It is a nasty teacher stereotype that damages our proffession. Secondly, I usually use my breaks to, you known, have a break. Definitely not reply to emails.