Your next major concern will be compatibility. It's not a shock that most businesses run on Microsoft Windows and use some form of Microsoft Office. Being able to use common third-party clients such as Microsoft Outlook can often be a concern, and even today, compatibility with Microsoft Outlook isn't necessarily guaranteed. This is especially true when sending and receiving meeting invites. It only takes one garbled meeting invite to realize how frustrating this can be in the real world. Even if using Microsoft Outlook isn't a concern, portability is. If the service is entirely web-based, then is there a means for me to take my email offline and send email when I connect?
MessageGears is a hybrid email marketing system that combines the security of an on-premises system with the scalability of the cloud. The service connects directly to any local or remote database, data warehouse, e-commerce system, or content management system. There is no need to extract, transform, or load customer data into the system or to move or replicate data. Features include subject line previews and testing, spam testing, and automation, drip and trigger campaigns.