Yesterday I changed to OH 2.4 and suddenly I receive emails triggered by my rule twice. Before it was working and I got only one mail as expected.
This is the line I am using in my rule:
sendMail("xxx@gmail.com", “Sonbas09_2”, “Sonbas09_2 motion”)
Is there anything changed for mails in 2.4?
2.4 is already quite old. I don’t remember reading about any problems with the Action for 2.4, but that Action has since been replaced by the new Mail 2.5 binding. So if there is a bug, the solution will likely be upgrading to the new binding.
The biggest thing I can recommend is to verify the Rule isn’t triggering twice. If it isn’t than you best bet is to upgrade to 2.5 M3 and use the new binding.
Oh really, so far I tried to use the release builds only 
But can I check somehow in 2.4 why it sends the mail with exactly the same content twice?
Or can I remove the binding and install it again, maybe this improves or something else?
As I suggested, add logging to check if your Rule is triggering twice. If it isn’t you are largely on your own.