Error on mail connector

I'm using Bonita Community 7.9.3

I'm facing a random error on a mail connector.

Sometimes it works ok and the mail is sent ok, and suddenly on a new case of the same process, the connector stays in "executing" for a while and then changes to "failed" (i see this in the portal with the admin user) and the mail is not sent.

This is the error i've found in the logs:

Groovy script throws an exception of type class java.net.SocketException with message = Unexpected end of file from server

....

....

Caused by: java.net.SocketException: Unexpected end of file from server

It is always that same error but it doesn't appear on all the cases of the process, only on some of them.

Any help would be appreciated.

Thanks.