This function was taken away almost 5 years from now because it was rarely used. I would suggest to replace it in a professional mail handling software or make your custom handler. i.e. you could try Sieve rules managed via Roundcube to have your own custom autoresponders.

I checked which other control panel can help with your problem and didn't get much success unfortunately.

This "usecase" is neither rare nor unique it is a CORE part of any business that works on the internet.

A real scenario:
1) a Customer orders a product of mine via a web form and choose Wire transfer as payment option
2) The form sends the order to orders@domain.com
3) The Auto-reply did check if the hidden text "ORDERFORMWIRETRANSFER" was present in the e-mail and did send back the Customer the bank's routing information via e-mail (only in that case)

Without that option all the mail sent to orders@domain.com receives back a reply containing the bank's routing information, including orders with payment via Credit Card ans spam messages.

Since when upgrading to Plesk Panel 11.5 in Home -> Subscriptions -> domain.com -> Auto-Reply, I no more have the option to reply only if the original e-mail contains a specified text.

Previously I was using this option to reply only to legitimate mail (because I autoresponded only to mail sent via a formmail in my domain and that formmail had an hidden field containing the required text).

Without that option, all the mail sent to the mailbox receives the auto-reply, including mail sent without the formmail (that doesn't need such autoreply) and spam (so I receive back a lot of bounces because spammers often uses fake sender addresses that cannot be autoresponded)

Replying only upon a specified condition doesn't seem to be a so unique scenario, considering also that option WAS present in previous Plesk versions.

Hope it's much clear now, but if you need further details, please do not hesitate to ask.

Thanks,
Davide