we have a Zimbra Mail server that was being used for 2 months now. the last week we faced a problem that the Public IP that was being used for our mail server started to be blacklisted and we couldn't send emails to many other domains.
we found that the Engineers who was responsible for Administrating our Public IP Block didn't configure a reverse DNS PTR.
we have changed the Public IP to another new one, we were able to send to some of the domains that we were blocked at but some others are still blocking, for example we can't send to gmail even that after we configured the New IP and Publish the new DNS reords we were able to send to gmail , but after 1 hour gmail bloked us again with this error message The mail system
: host gmail-smtp-in.l.google.com[18.104.22.168] said: 550-5.7.1 [xxx.xxx.xxx.xxx] The IP you're using to send mail is not authorized to 550-5.7.1 send email directly to our servers. Please use the SMTP relay at your 550-5.7.1 service provider instead. Learn more at 550 5.7.1 http://support.google.com/mail/bin/answer.py?answer=10336 ey7si20778000wib.30 (in reply to end of DATA command)
also below are some other errors we recieve from different domains
The mail system
: host maila.aljazeera.net[22.214.171.124] said: 550 5.7.1 Recipient not authorized, your IP has been found on a block list (in reply to RCPT TO command)
: host relais-ias89.francetelecom.com[126.96.36.199] said: 550 5.7.1 : Client host rejected: Your message was rejected due to spam filtering. Please see http://www.sophos.com/security/ip-lookup?ip=xxx.xxx.xxx.xxx (in reply to RCPT TO command)
any help or suggestion please, and can you please direct us to a place where we can learn how to make our server less likely to be blacklisted.