Postfix - Amavis erroneus SPAM

Deal, a software that control an hardware has to send alarm mail when
something happens. Starting from two weeks ago, the alarms stops to be
sent and checking in the mail server logs I see the following message:

Mar 12 09:03:57 mailserver amavis[14797]: (14797-01) Blocked SPAM
{DiscardedOpenRelay,Quarantined}, [150.217.XXX.XXX]:3685 [150.217.XXX.XXX] <mail@mydomain> ->
<mail@externaldomain>, quarantine: M/spam-M9145UbnjoSh.gz, Queue-ID: CB9E3837E0F, Message-ID:
<5E7A686C7FD740989C918BF83AAEECF3@6204eng1>, mail_id: M9145UbnjoSh,
Hits: 6.57, size: 639, 551 ms

The alarms are blocked as SPAM. Is there a way to instruct
amavis/postfix that this mails aren't SPAM?