To set up mail correctly in different email clients (Outlook, Thunderbird, ..) you need to set up the port numbers correctly. These are as follows, depending on the type of protocol (IMAP or POP3) and whether you have chosen a regular or secure connection.

IMAP

Incoming mail

No encryption

Port: 143

SSL encryption

Port: 993

Incoming mail

No encryption

Port: 587

STARTTLS encryption

Port: 587

POP3

Incoming mail

No encryption

Port: 110

SSL encryption

Port: 995

Incoming mail

No encryption

Port: 587

STARTTLS encryption

Port: 587