Symptoms
-
Plesk server is hosted with OVH SAS.
-
When an email is sent to Outlook or Hotmail recipient addresses, the following error is found in
/var/log/maillog:550 5.7.1 Unfortunately, messages from [203.0.113.2] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140).
-
Recipient addresses from other mail services providers are not affected.
Cause
Recently, UCE Protect has placed over a thousand new ASNs on their blacklist. One of OVH SAS' ASN has been listed on the UCEPROTECTL3 blacklist.
Resolution
Contact OVH to get a new IP that is not blacklisted or set up an External SMTP server in Plesk as per the article How to configure an external SMTP server in Plesk:
- For AWS SES it's required to set up your SES account, get out of the sandbox, get your SMTP credentials and apply the article above.
- For SendGrid it is required to adjust Postfix configuration as per How to configure Postfix on Plesk server to send emails using SendGrid