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
