Networks

I hadn't heard of Heluna, but based off the web site the pricing and plans look good. Hopefully someone with experience using it will reply as you wouldn't want to go with a provider that gives you trouble.

As for alternatives, check out spamhero. Cost is $60 per year for unlimited mailboxes and domains. They have a shared quarantine (individual if you play more). They have lots of positive feedback over at Spiceworks so I recently checked it out for one of my clients and I've been very impressed. For the price I was expecting a limited interface but everything has been very smooth and easy.