- Plesk for Linux
- Email remains in mail queue: Postfix tries to send many emails to the external recipient but only one email was sent initially
Many following records appear in /var/log/maillog* files:
CONFIG_TEXT: postfix/smtpd: C7697151C60: client=mail-it0-f49.example.com[203.0.113.2], sasl_method=PLAIN, email@example.com
postfix/smtp: C7697151C60: to=<firstname.lastname@example.org>, relay=mx.spamexperts.com[203.0.113.2]:25, delay=38, delays=0.67/0/3.6/34, dsn=4.0.0, status=SOFTBOUNCE (host mx.spamexperts.com[203.0.113.1] said: 550 The sending IP (126.96.36.199) is listed on https://spamrl.com as a source of viruses. (in reply to end of DATA command))
IP address of the server got in blacklist https://spamrl.com due to outgoing spam and/or viruses being sent from it. Since another SMTP server rejects the email with soft-bounce status, Postfix tries to send it for 3 days with 5-15 minutes time interval according to default settings.
Find and exterminate the source of spam according to the article How to find the source of spam .
Remove IP address of the server from the blacklist https://spamrl.com according to the instructions on this website.