Multiple MX Records For Same Domain Email

Right, I have my email address (say email@domain.co.uk) connected to my DirectAdmin controlled server.

I have an the simple email services provided by 1and1 that I haven't used for ages.

I am a bit confused how multiple MX records can be used, so far I have edited my DNS record file for domain.com to look like this:

Code:
domain.co.uk.14400INMX5mx00.1and1.co.uk.
domain.co.uk.14400INMX10mx01.1and1.co.uk.
domain.co.uk.14400INMX0domain.co.uk.
If im not mistaken the above show the email server domain.co.uk is connected to (domain.co.uk) is the primary server, with 1and1 2nd and 3rd.

However if I changed the priorities all to the same value, i.e "0" would that mean the mail is delivered to all?

My ideal solution would be, if the primary server was down, send mail to secondary, but that leads me to another problem. When I want to check mail with Thunderbird its connected to imap.domain.co.uk and not imap.1and1.co.uk, so the problem now is mail split over two servers....! I would like a redundant system, to ensure email is online 99.999% of the time.

So my question is, what are peoples current solutions with multiple MX records, and how have they achieved 99.999% uptime of emails.