Are you also a Linux user? Here's an article to help you protect your systems against uninvited intruders.
Need to solve below : 1) When my customer read the email from Microsoft Outlook [POP], the zimbra webmail still show the email is unread. Need to solve this issue? 2) host  said: 550-5.7.1 [ 12] Our system has detected that this message is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to Gmail, 550-5.7.1 this message has been blocked. Please visit 550-5.7.1 550 5.7.1 for more information. y13-20020a056000168d00b00222d108e8d5si6028704wrd.542 - gsmtp (in reply to end of DATA command) Thank you