I am testing the K-9 Mail client with my own hosted mail servers. While reviewing the header information from a message I send to myself with K-9, I noticed that the message is originating from 127.0.0.1 with the FQDN of the connection I am using at that moment.
Is there a way to prevent this?
Reason for asking is that if I would be on like a public WiFi which has not the best reputation, I feel this might potentially put this message to spam, as that FQDN of the ISP is actually not a trusted sender for my domain. And secondly, I not always want to share where I am and what connection am I using.
It’s your mail server that is adding this header to the message, not K-9 Mail. You can most likely configure it to not put the real IP address/hostname there.
For Postfix see e.g. email - How to modify Receive header in Postfix - Server Fault
This worked perfectly with this header adaptation for Postfix. I actually ignored it at first because another mail client I was testing didn’t do it. Same servers. But strictly spoken this User_Agent information is according to standard indeed. In other words K-9 was correct.
I now changed it to the IP address and FQDN of the web server hosting the webmail. Which is also in the SPF records etc.