Problems with Mail after migrating from plesk 9.5 to plesk 10.4

[SalvadorP]

Recently migrate all domains from one server to another with plesk plesk 9.5 to 10.4, both with qmail, and specifically one of the domains that use a php script to do mailings, which worked smoothly Plesk 9.5, and 10.4 plesk I have noticed that when you are shipping over 1000 mails (approximately), there are many of them who do not reach their destination, not giving any error message, it may be due?