IAMP servers in FreeBSD for ISP

[Francisco Reyes]

Anyone care to share what IMAP servers they have found to scale best?

We are currently using courier and at times it seems it really will not 
scale well into thousands of emails.

We have basically one setup with self contained machines that do all the 
work and a second setup where we break the load into MX machines, NFS to 
store the maildir for courier and front end machines to run courier and NFS.

We can handle hundreds of accounts in the self contained, more or less ok 
(depending on the mix of pop or imap).

The second setup is more complex to meassure since the load is distributed. 
The biggest problem with this second setup is that the front end machines 
end up needing to mount several of the Maildir NFS servers and we have found 
that one of the NFS servers going down can affect all of the front end 
machines.

What have others found to scale well and what kind of hardware are you 
using?