This is what your server responds with:
=== Trying mail.bargiona.eu:25...
=== Connected to mail.bargiona.eu.
<- 220 free.subnet01221743.vcn01221743.oraclevcn.com
-> EHLO me
<- 250-free.subnet01221743.vcn01221743.oraclevcn.com Hello 1.net-203-0-113.example.com [203.0.113.1]
<- 250-SIZE 52428800
<- 250-8BITMIME
<- 250-PIPELINING
<- 250-PIPECONNECT
<- 250-CHUNKING
<- 250-STARTTLS
<- 250 HELP
-> MAIL FROM:<[email protected]>
<- 250 OK
-> RCPT TO:<[email protected]>
<** 550-Rejected because 203.0.113.1 is in a black list at zen.spamhaus.org
<** 550 Error: excess volume; https://check.spamhaus.org/returnc/vol/140.204.12.41/
-> QUIT
<- 221 free.subnet01221743.vcn01221743.oraclevcn.com closing connection
=== Connection closed with remote host.
So all the mails from any source are being rejected because you reached a limit in Spamhaus.
550-Rejected because 203.0.113.1 is in a black list at zen.spamhaus.org
550 Error: excess volume; https://check.spamhaus.org/returnc/vol/140.204.12.41/
Take a look to this post to check a few options to fix it: