In the top menu bar click Mail.

Select the Preferences option.
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Click the @ Accounts option in the top bar.

Click the Server Settings tab.

Edit the Incoming Host Name field to the following:

For POP3: pop.fusemail.net port 995 with TLS/SSL

For IMAP: imap.fusemail.net port 993 with SSL

Edit the Outcoming Host Name field to: smtp.fusemail.net port 587 with TLS/SSL

To edit the Incoming/Outgoing ports, UN-check Automatically manage connection settings. The Port field and Use TLS/SSL checkbox then appear.

Edit as needed. It's recommended to use incoming values of port 993 for IMAP and 995 for POP.

When finished, click the Save button.