The host did not solve the problem, could anyone give us a clue …?

The outgoing emails from my clients are as captured by an antispam firewall, they receive a wrong answer "550 This message has been categorized as SPAM and can not be sent" if their message looks very spammy (content, object, contacts, etc.,)

So this broke our service and my HTTPME host has not fixed it yet

Here is the mistake that customers receive with SOME messages that they try to send. Does anyone have a clue so that I can tell these guys where to look?
My clients have different ISPs, different email clients, etc. but they are all on the same server.
I translated it a bit in English

From: Administrador del sistema
Posted on Tuesday, November 28, 2018 at 9:54. m.
AT: ****************
Subject: Sin entregar: ********

Algunos de los destinatarios no recibieron su mensaje.

Asunto: **********

Enviado el: 28/11/2018 09:54 a. m.

No problem to locate the recipients:

& # 39; ********** & # 39; to 28/11/2018 09:54 a. m.

550 This message has been classified as spam and can not be sent.