Problems Sending out Emails - All to Spam Folder

Hello there, I've been running my ISPconfig 3 server for about 4 months now, and I've been having an issue with outgoing emails, they always go into the Spam Folder for GMAIL/Hotmail and all big services, any idea why would this be ?

I used this guide for the installation https://www.howtoforge.com/tutorial/ispconfig-automated-install-script/ on Ubuntu 16.

Thanks,
Indicium

 

Did you set the ptr for your ipv4 and ipv6 to the name of your mailserver? https://blog.schaal-24.de/mail/emails-richtig-versenden/?lang=en

 

As stated above and check mxtoolbox that your domains are not blacklisted.

 

Updating txt record to
v=spf1 a mx includeOMAIN.com include:mailgun.org ~all
resolved the issue quite nice. Thanks for the help.