[imp] Scalability of rate-limiting?

[Wil Cooley]

We are considering implementing limits on recipients per message and per 
time period using the features that we have now in IMP. We have a fairly 
sizable user base; it's hard to estimate concurrent connnections with 
HTTP being stateless and our IMAP connections being cached with up-
imapproxyd, but I'd guess we peak around 3k concurrent users across 5 
webmail front-ends.

Assuming we use the SQL driver for permissions and not DataTree, what 
kind of additional overhead should we expect between the permissions 
check and the outgoing e-mail logging?

Are people using these rate-limiting features with sizable installations 
with success?

Wil