As a first step open the application menu in the right. Here is in the Preferences sub-menu the "Account Settings ..." point. For earlier versions, when it was still top menu bar, then this could be found in the Tools menu.

Here you can see the mailboxes, but I do not have to deal with. On the left below is a "Mailbox Operations" button, select the "Add Mailbox" option.

In the next window fill out all three field empty, then click the Continue button.

Then "Manual settings".

Fill in the required fields as follows: connection port, protocol, authentication mode, and the user name field enter your full email address as shown:

IMAP | mail.mik.uni-pannon.hu | 993 | SSL / TLS | Normal password
SMTP | mail.mik.uni-pannon.hu | 465 | SSL / TLS | Normal password
After that, you just need to click the Finish button!