Primary And Secondary Servers (web And Mail)

I have 2 servers 1 US and 1 UK.

What I wanna do is synchronize both of them using rsync. Once they've got synchronized, the UK will be the primary server and US will be secondary, in case the UK goes down.

my questions are

1. Is it possible that when the UK goes down, the A records for domain.com automatically switches to the US server so it can take over while UK is down.

ie. UK ip 112.113.114.1
US ip 222.111.444.5

domain.com A records = UK ip when up... but when UK is down, A records automatically changes to US ip.

2. And when the UK server goes up again, whatever changes made to US server will be pushed to UK. May it be files, accounts or e-mails.

I.E.

UK and US are synchronized every 30mins. UK and US both have e-mails 1-10.

Just before the sync time, UK server received an e-mail 11-15 then goes down. So the US Server will take over but do not have 11-15 mails, since it was received before sync time. During the UK downtime, US server received e-mails 16-20.

When the UK server goes up, will it be possible to sync both servers that both of them will have the e-mails 1-20?

I hope you get my point...

If these are not feasible, what can you advice as an alternative solution. All I want is to avoid downtimes, especially with mails as the business relies on this.