One of the most important compatibility factors to consider with email is the mobility question. How often do your employees need to access email via mobile devices? That's an important issue because most email hosting providers deliver some kind of web client usable as a default inbox. Almost all of these can be accessed via a mobile device, so if your employees don't need to access their emails on the road that much, then such mediocre clients are probably fine.
MailUp gives businesses the tools to send newsletters, promotional emails and transactional emails from one platform. The MailUp email and SMS delivery platform combines email marketing tools with SMTP relay for transactional emails and plugins for e-commerce, CRM and CMS systems. The service's pay-per-speed pricing is designed for midsized companies looking to scale their email marketing efforts.