As suggested by previous posters, I have added the -R flag in my /etc/xinetd.d/smtp_psa in order to prevent outgoing reverse ident connections. This has made my users much happier - their mail gets sent in seconds rather than minutes and they no longer get timeout messages.

However, this means that every time I make a configuration change, I need to go in and reapply that edit by hand, because that file gets overwritten by Plesk.

Is there any way around this problem? Is there a template file somewhere Plesk is using to generate that file that I could modify?