I've been on vacation, I tried  $conf['maillog']['use_maillog'] = 
false and now it's pretty fast.

Thank you

And have you followed horde/docs/PERFORMANCE?  Since I am not seeing 
any particular slowness on my system, and there are absolutely no 
details in this report, I am going to close.  If someone can identify 
the particular code/component that is causing slowness, a bug report 
should be opened with that information.  But this report is way too 
broad.

Try setting:

$conf['maillog']['use_maillog'] = false;

in imp/config/conf.php

I have the same problem that g.tranelli has described, it's slower RC3 
is slower than ALPHA in viewing message. And NAG-RC3 is slower than 
ALPHA viewing notes, too.

Please help me because i want to put it in production as soon as possible.

I've disabled GeoIP and the slowness continues on and on.

By me I must be in the php source, but I don't have enough knowledge 
about PHP to verify

I'm not having any problems on my system though.  Make sure you are 
not showing the country flags since the inability to resolve addresses 
via a nameserver will slow down page views.

yeah, it's not a very specific report, but it does sound like we 
should try and do some tuning either of the final releases or just 
after.

I'm have both imp 4.0-RC3 and 4.0-alpha installed on the same server 
as virual hosts.

When I click a message in imp4.0-RC3 is very slow, when I click a 
message in imp4.0-alpha is very fast