Plesk Mailserver Error Connecting

[OliverSadler]

When connecting to the mail server through Apple Mail, I get an error after about 30 minutes saying that the connection to the mail server on port 143 could not connect. I have tried using it with SSL (port 993) and also used the mail server with postfix and qmail. The email does occasionally connect and receive emails randomly. I have checked that both ports are open and are being allowed through the firewall.
Any help would be appreciated.

 

[Daniel H]

Did you try to delete your account in apple mail and recreate it? Had same problem but with my iPhone last month.

 

[OliverSadler]

I have tried on multiple machines with different internet connections and also deleting the account and setting it up again