Sysadmin Has anybody tried Zimbra

IP, domain, analysis of the sent mail messages before or mixed. Nobody knows as it is Google's and Microsoft's secret how they rank.

The only thing a webmaster can do is use a clean server, an ip (clean) for a long time, same goes for the domain. Sign up for Gmail and Hotmail postmaster tools. Never send spam duh!. Never send bulk shit(if yes only bulk according to the guideline of both company's above). etc.

For example if some dif shit already sent spam or bulk mail in the past with the same domain (Previously registered and later terminated) or ip. You could ranked for spam right away.

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Even if your mail is legit and your server isn't compromised.
It is very difficult to clean this up, if you already been listed on several blacklists. (Without your fault).

 

I didn't test it yet