Syncing your contacts with your iOS device's address book
The cardDav protocol allows you to sync your mail.com contacts with
the contacts app on your iPhone, i.e. any changes made on your iPhone will be available on
mail.com and vice versa.
On your home screen, open your iOS Settings
Select Accounts & Passwords.
Select Add Account.
Select Other.
Select Add CardDAV Account.
As server, enter "carddav.mail.com".
Add your mail.com email address and your password.