[sync] Problem with Active Sync (very slow and disconnect with Outlook 2013 clients)

[Soporte Tecnico]

Hi I have a little problem with my ActiveSync configuration, I have the
default conf on my horde installation, and I have virtualmin server
installed on my vps, and I have some accounts with more than 500MB size
inbox, when I configure Outlook 2013 with these accounts (activesync type)
 I have the problem that the sync is very slow ( I have sufficient bandwith
on each point)  but the sync is very slow...
the server sync 30 or 40 emails each time but after 10 minutes the sync
stop, and I need to restart Outlook again to start the sync....

I think that could be a server perfomance problem but I didn´t find any
recomended configuration for apache...

when I see the apache logs I see some errors like this...

[Tue Jul 15 09:56:20 2014] [warn] [client 190.14.142.26]
(104)Connection reset by peer: mod_fcgid: error reading data from
FastCGI server
[Tue Jul 15 09:56:20 2014] [error] [client 190.14.142.26] Premature
end of script headers: rpc.php

There is somebody could give me some help...?