Prioritizing among MX records

[Jan Kozánek]

Hello,

I'd like to ask if anyone knows whether numbers in MX records are just 
positional values or real priority numbers.

Let's say we have an example like this:

bogus.com.    IN    MX    10    primary.bogus.com.
bogus.com.    IN    MX    60    backup.bogus.com.
bogus.com.    IN    MX    65    last-hope.bogus.com.

Does it mean anything else than that under any circumstances, if mail 
relay will fail with primary.bogus.com, relaying will be tried to 
backup.bogus.com IMMEDIATELY and if that fails, it will be IMMEDIATELY 
tried to last-hope.bogus.com?

Is number of delivery retries to each of the mail servers dependent 
solely on the sending SMTP server's software?

Reason for my question is that some time ago I found a material quoting 
that the priority number in a way affects also the number of failed 
retries a relaying SMTP will try with each mailserver, before falling 
back to the one with lower (higher number) priority. And, to my 
surprise, while testing, I discovered corelating speed-ups/speed-downs, 
which could justify the above statement.

Thanks for clarification,
Regards

-- 
S pozdravem/Best Regards,
Jan Kozanek