I am setting up a phony user in EXIM to forward newsletters to a list of recipients. For some internal reason, I want it to wait 10 seconds before sending each mail(sending too rapidly triggers spam filters). Can I add delays into a .forward file?
Whose spam filters are you triggering? Some sites will greylist on initial contact, but a 10 second delay will not likely help. Normal queue and retry will work with this setup.
You might be able to do this with a second EXIM configuration and rate limiting calls between the servers.
The queue options might also help, but would impact other users. A combination of queue_only_domains, and a low queue_run_max might help.
If your client is compliant, then a condition delay for the client in the configuration might also help.