I don't know where actually to look for help. Is there any service at Barracuda Networks where I can file problems with sending emails to barracuda-protected websites? I have checked whether our SMTP outgoing IP is not listed at any significant RBLs, but it seems to be clean...
I'm running a server hosting multiple domains, and today one of my clients asked me about Post Delivery Failure notification being received from the address, which she could send emails just few days ago. I have verified, that she is unable to send any email (so it's not about heuristics) to any email in the specific domain.
Here is the message that she received. She was sending emails from firstname.lastname@example.org.
Content-type: text/plain; charset=us-ascii
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
host d300367.b.ess.de.barracudanetworks.com [18.104.22.168]
SMTP error from remote mail server after end of data:
550 permanent failure for one or more recipients (email@example.com:blocked)
Reporting-MTA: dns; silvercube.pl
Remote-MTA: dns; d300367.b.ess.de.barracudanetworks.com
Remote-MTA: X-ip; [22.214.171.124]
X-Remote-MTA-smtp-greeting: X-str; 220 mail.ess.de.barracuda.com ESMTP (mx1.eu-central-1a.ess.aws)
X-Remote-MTA-helo-response: X-str; 250-mx1.eu-central-1a.ess.aws.cudaops.com Hello mx.silvercube.pl [126.96.36.199], pleased to meet you
X-Exim-Diagnostic: X-str; SMTP error from remote mail server after end of data: 550 permanent failure for one or more recipients (firstname.lastname@example.org:blocked)
Diagnostic-Code: smtp; 550 permanent failure for one or more recipients (email@example.com:blocked)