Sending and receiving email with your iOS device
Here we use "test@dynu.biz" as an example.
Step 1: Add an email account

If you are using iOS 11 or later, go to
Settings then
Accounts & Passwords then
Add Account.
If you are using iOS 11 or earlier, go to
Settings then
Mail, Contacts, Calendars then
Add Account.
You need to choose
Other to add a new account.

In the following window, choose a name for your account, which would be the name
that people see when they receive emails from you. Here we will just use "John Doe".
Then put your email address as the user name and the password you that set up for this account.
Description is a friendly name that you give to the account, it is only visible to you in the mail application of your device.
Step 2: Set up incoming mail server

As you continue, you will see this window asking for incoming and out going mail server info.
For IMAP account, choose
IMAP
and use
yourname-extension-mail.dynu.com
as mail server (in our case, dynu-biz-mail.dynu.com). You need to put in user name and password one more time.
Please note that the username is your full email address, test@dynu.biz in our case.

Use
yourname-extension-smtp.dynu.com
as mail server (in our case, dynu-biz-smtp.dynu.com). You need to put in user name and password one more time.
Please do enter the username and password even if the application says it is optional.
Step 3: Verify account information to use SSL

Now you can see your account in the
Accounts list.
You just need to verify one last time the account information,
particularly the information of the incoming server and outgoing server.

Click on the email account that you just set up in the list of email accounts,
then click on
Account test@dynu.biz to go to the account settings.

Go to
SMTP yourname-extension-smtp.dynu.com then
yourname-extension-smtp.dynu.com, enable
Use SSL
and make sure that SMTP server is
yourname-extension-smtp.dynu.com
port is
587.

Go back to account settings, in
Advanced
tab, verify the information of IMAP incoming server. Enable
Use SSL and make sure that IMAP server is
yourname-extension-mail.dynu.com
port is
993.
Now we will be able to send and receive email using test@dynu.biz.
NOTE:
If you are using POP3 protocol, please change the incoming server address to
yourname-extension-mail.dynu.com, and
POP SSL port 995. If you are using non SSL port, please refer
here
for port information.