Step: 1 (Add your IMAP email account)

Go to Settings > Passwords & Accounts > Add Account

Select Other > Add Mail Account (to create a new email account)

Step: 2 (Enter your Email Address)

Fill in all the required fields, 

Name: Your Own Name

Email: example@yourdomain.com (Your own email address)

Password: Your own email password

Description: Yourdomain 

Step: 3 (Account Setup)

Select IMAP, fill in all the required fields for the Incoming and Outcoming mail server then tap Next to verify the email account.

Host Name: mail.yourdomain.com 

Username: example@yourdomain.com (Refer to your own email account)

Password: your email password

Verify the email account. After the verification process makes sure to enable the Mail, then tap Save.

Step: 4 (Configuring SSL)

Go to Setting > Password & Accounts > click the Description (your own email domain account) > Account > Outgoing Mail Server(SMTP) > mail.yourdomain.com.sg > enable Use SSL

Outgoing Mail Server:

Server Port: 465

After the verification is done, go back to Account and select Advance. In the Advance setting, there is an Incoming Setting > enable Use SSL 

Incoming Mail Server:

Server Port: 993