Setup:

• Odoo9 on our own server
  

• Office 365 for sending E-Mails from odoo (works well)

• SPF Record set in the DNS: v=spf1 ip4:188.68.xxx.xxx include:spf.protection.outlook.com ~all

Problem description and analysis:

• Sending normal E-Mails from Odoo works.

• Sending E-Mails with attachments are often considered as spam at the recipients end

• https://www.mail-tester.com/ does not see anything bad about them.

• Odoo does not send a readable Text version with that email. Only HTML. Could that be a reason?

• • HTML only + Attachement = Evil?

• Normal emails sent with attachments over the same server with the same content are not classified as spam!