[RCU] Slow displaying INBOX with thousands emails

[Alexey]

> So, you're showing the imap server timings. Note the response need to
> be sent and parsed by the client.
Yes, and since my client is roundcube I wrote to this maillist, to solve 
this performance issue.

> hint: you can set $config['performance_stats'] = true
mail [1.2 МБ/1.5 МБ]: 0.1386 sec
mail/getunread [929 КБ/997 КБ]: 0.0092 sec  (it's probably for showing 
counters in folders tree)
mail/list [1.3 МБ/52 МБ]: 1.0174 sec