Mailing solution

Hi,

I have been using Action Mailer and Mailer Queue as a mailing solution
on my website. But since we foresee lot of email marketing such as
notifications, daily,weekly and monthly updates, I was wondering I
should offload the server of these activities.

Now, what are the options that I have? I tried phplist, it didn't really
work for me. What are you people using / what do you suggest. These
mails can be like News Letters, n such so , I would use HTML emails.
Please let me know of the options, that will be great!

Regards,
SG