Form sends the contact email but they are not delivered, they return with an error

Hello,
Since February 18th, the form has stopped sending contacts that arrive on it. It worked perfectly for 3 months and since the 18th it started to have this problem.
The email I use for sending works if I send it directly via the webmail box to any other email, it just doesn't send the contacts that arrive via the form. I contacted the hosting server support and no problems were found with the email. We did all the tests sending and receiving via webmail and they all work perfectly. But it doesn't work on the form, even if you change the sending email to another, it doesn't send either, it just returns the error (image attached). So I need help figuring out what could be going on? Thank you very much in advance. Tks

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