Distributed or centralized mail configuration?

[Haim Shvaytser x2085]

What are the advantages/disadvantages of a distributed mail configuration 
versus a centralized mail configuration? Which is easier to maintain, which 
is more secure, and which is more "standard"?

What are the main reasons for a domain to switch from a distributed mail 
configuration to a centralized mail configuration? Do you know of a domain
that actually switched?

haim at utdallas.edu