Select and hold the Mail icon and select “remove app,” then go to the App Store and download the app again onto your phone. I didn’t even have to set up my email account in the Mail app again; it was already there. I just had to go into the Mail settings and activate it. After that, I could send and receive emails through Mail app again.
Note: AOL and Verizon customers who need to update their account settings after AOL's recent change to their server settings should see the section Update your email settings in Outlook for Mac. When checking your encryption settings, make sure they're set to SSL, SSL/TLS, or Auto and not TLS only. Add a new account quickly
After you enter all the necessary settings, you'll be able to send and receive Mail.com messages using your preferred email client, and manage your Mail.com inbox and other folders. After setup, you can continue to use all the features available at the Mail.com website interface in a browser as well.