1. After logging into your mailivery account click "Add new account" on the left. 

2. Select "Use any other account".

3. Now type in your IMAP/SMTP settings and password. You can ask your IT-admin or search the web for the IMAP settings of your public e-mail provider.
You should only use encrypted ports with mailivery. Encrypted ports for SMTP are 465 or 587; for IMAP 993.

Here are a few examples:

IMAP: 993 / SMTP: 587
IMAP: 993 / SMTP: 465 or 587
IMAP: 993 / SMTP: 587

You might have to generate an app password for mailivery and use it instead of your e-mail password. You can generate app passwords in your e-mail account security settings. Yahoo as an example offers app passwords when you go to account security, generate app password, select other, type in "mailivery" and generate.

4. Click "Test & Save"

5. Done