Asynchronous jobs in Rails

Hi,

I have been researching about this for couple of days now. My rails
application needs to send email notifications to large number of
customers. Before sending the message, application customizes content
for each recipient. The requirement compels me to call ActionMailer’s
deliver method for each email address.

I would like to send notifications asynchronously. I looked into
backgroundRB. I have been playing around with it for almost two days
and I can’t get it working on cygwin. However, my main concern is the
poor performance of backgroundRB for moderate or high scalability
needs.

I also looked into Threads in ruby. Since rails is single threaded and
especially ActiveRecord is not thread safe, I dropped that idea too.

What are the options generally used for asynchronous jobs in rails ?
From google search I find only two options mentioned above. Please
tell me your experience with either of them. Is there any other
solution that I have overlooked ?

Thank you!