Symptoms
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Unable to send emails using PHP Scripts.
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The following error shows up in
/var/log/maillog:Jan 30 10:38:40 server psa-pc-remote[10314]: 808834E4966: from=john.doe1@example.com to=john.doe@example.com
Jan 30 10:38:40 server postfix/smtpd[10391]: bare <LF> received after DATA (2852 bytes) from server.example.com[203.0.113.2]
Jan 30 10:38:40 server postfix/smtpd[10391]: disconnect from server.example.com[203.0.113.2] ehlo=1 auth=1 mail=1 rcpt=1 data=0/1 commands=4/5
Jan 30 10:38:40 server postfix/cleanup[11992]: 808834E4966: message-id=<>
Jan 30 10:38:40 server psa-pc-remote[10314]: Message aborted.
Jan 30 10:38:40 server psa-pc-remote[10314]: Message aborted.
Cause
Plesk 18.0.58.1 hotfix included a fix for CVE-2023-51764 vulnerability which does not allow mail scripts to end with a blank or bare line as this is a potential vulnerability. If the script creates bare lines at the end, the email will fail to send for security reasons.
Resolution
Adjust the email scripts in order to avoid newlines at the end of the body.