If you are having problems such as "Unknown SSL certificate" try updating POP3/IMAP server details. Visit this page, for details and follow these steps just to update your existing email settings:

Update existing email settings - Samsung Galaxy S7

1. From the home screen, tap Email.

   Note: If the shortcut is not available, tap Apps, then scroll to and tap Email.

2. Tap MORE.

3. Tap Settings.

4. Tap the email account.

5. Scroll to and tap Server settings.

6. The email settings are displayed and may be edited.

   When finished, tap DONE.

7. The email server settings have been displayed.

New email account settings - Samsung Galaxy S7

To configure personal email server settings, follow these steps.

1. From a Home screen, navigate: Apps  > Samsung folder > Email.
    These instructions apply to Standard mode only.
2. From an Inbox, tap the Menu icon (located in the upper-left).
3. Tap the Settings icon (gear located in the upper-right).
4. Tap the appropriate account.
5. From the Advance settings section, tap Server settings.
6. From the Incoming server section, configure the following then tap Done:
    The available, settings may vary depending upon the email account type.
   • Password
   • POP3/IMAP server
      If you're not sure what your server info is, visit this page.
   • Security type
   • Port
7. From the Outgoing server settings configure the following then tap Done.
    The available, settings may vary depending upon the email account type.
   • SMTP server
   • Security type
   • Port
   • Require sign-in
   • Username
   • Password