Different people and organizations or companies have different needs and that can make some the worst for one and the best for another. If 512K encryption is what you want and your email service doesn’t have it then it isn’t the best for you. Look around the net a little and you will find what you need.
As I said at the start, what best is pretty much subjective. Put a little time into checking out email and you will find the best email service for you.
If you do a search, you can find many companies online that sell or provide email marketing services. Some have a large range of services that will help your marketing campaigns with autoresponders, conversion tracking and other resources. For the best email service you are going to want your own dedicated email server and some sending software or email blast or broadcast software.
You can set up a web based email marketing campaign to send newsletters, follow up email messages, campaigns, broadcasts and much more that will make you a ton of money.