[Dovecot] Increate proc limit and default client limit

data/conf/dovecot/dovecot.conf

@@ -232,7 +232,7 @@ service managesieve-login {
 }
 service imap-login {
   service_count = 1
-  process_limit = 500
+  process_limit = 10000
   vsz_limit = 1G
   user = dovenull
 }
@@ -347,3 +347,4 @@ auth_cache_negative_ttl = 0
 auth_cache_ttl = 30 s
 auth_cache_size = 2 M
 !include_try /usr/local/etc/dovecot/extra.conf
+default_client_limit = 10240