Your mail server for both incoming and outgoing, is always your domain name preceded by "mail."
Enter exactly what comes after the @ in your email address.
An example to make it clear.
The POP3 mail server for info@Bacan.com would be mail.Bacan.com
IMPORTANT
If you use your server's IP address, it could fail in the future since IP addresses can change. So it's always better to use your domain name as the incoming and outgoing server.
What does the incoming mail server mean?
To receive email for your domain, you need an incoming mail server. This service is included in your hosting plan. If you want to have email linked to your domain, you inevitably need an incoming mail server.
What is an incoming mail server?
It is a computer program that runs 24 hours a day, 365 days a year, so you can always receive emails sent to you by your clients or contacts. The server we use is called Exim. It is the most widely used server on Linux servers. It is stable and very fast so your email is always available.