[Dovecot] Increase process_limit to 500, thanks to @mritzmann

data/conf/dovecot/dovecot.conf

@@ -213,6 +213,7 @@ service managesieve-login {
 }
 service imap-login {
   service_count = 1
+  process_limit = 500
   vsz_limit = 256 M
   user = dovenull
 }