Google Apps for Business is good and affordable. $5 per email address. They only charge per email address, so you can add multiple domain support to each addres

Google Apps for Business is good and affordable. $5 per email address. They only charge per email address, so you can add multiple domain support to each address. Just in case, they do offer phone support that is very helpful for emergencies. We have been using them now for several years and have never had a major problem. Several months ago we had to merge another Google Business account into our existing account and late on a Saturday night we had a support rep working with us through the entire process to minimize downtime and also ensure we didn't lose any email along the way. They followed back up with us several days later to see if everything was working properly and if we had any more issues. I was pleasantly surprised considering the horror stories you hear about Google in general.