@yurividal
I would highly suggest not using the Docker image and installing osTicket on an actual server/VM. I've seen many posts about all sorts of issues with the Docker image. We did not develop nor maintain the Docker image so it's not really recommended.
If you install osTicket on an actual server and can still replicate the issue then post back here with an example raw email (including headers - after redacting any sensitive info of course).
Cheers.