Microsoft’s closest rival is winning rave reviews with its G Suite apps. If you enjoy using Gmail as your mail client, along with Docs and Hangouts, this might be it for you. Even the cheapest plan at $5/user/month comes with 30 GB storage, business email through Gmail, video and voice messaging, group editing on docs, sessions on Hangouts and shared calendars.
While most businesses will have such suites in place, it often falls to the email service to provide an additional layer of anti-phishing and anti-malware protection. Our reviews found a surprising variance in this department, however, ranging from very robust to completely non-existent, so be careful. Since it's such a huge liability for business owners, this could be one of the most important factors in terms of background features. At the very least, it's better than filing an insurance claim or outright losing funds due to simple social engineering tactics.
If privacy is your number one concern, perhaps you should go with Protonmail. You can upgrade to an email with your domain easily on a web interface under “Protonmail Plus” or “Protonmail Visionary” plans. However, the plans can be rather expensive, as getting only 20 GB storage space could cost you at least €24/user/month/yearly. Most email hosting providers retain your emails for months even after you delete your account. This Swiss email provider will destroy all your data when you delete your account.