Email distribution companies

[James Laver]

At $work, we have a newsletter that goes out weekly and frankly, it's
becoming a bit of a pain to manage, we just don't have the time to
fiddle with tweaking mailservers.

The newsletter is currently quite small, readership of about 4000, but
over time it's going to grow and for less hassle, it would be nice to
stick with the same company.

Can anyone recommend a decent company for taking care of email
distribution like this, on a relatively small scale?

Thanks,
--James