No longer receiving emails

I am no longer receiving emails, last email I received was on Monday.
Error message I get is:
Attempt to connect failed.
This could be caused by temporary server unavailability or incorrect settings.
I have made no changes to any settings and I can access my emails through the webmail of Telstra, where the email account is from.

This could be caused by temporary server unavailability or incorrect settings.
I have made no changes to any settings and I can access my emails through the webmail of Telstra,

As you haven’t changed anything your end as you advised, then could just be the server mailbox end technical issue connecting from mail clients currently, as per you are getting “temporary server unavailability” as part of the error, so that will normally automatically fix itself when the other end is resolved. You would just eg: close and reopen eM Client every hour or so till ok.

However what are your eM Client mail account Telstra settings via “Menu / Accounts” just to check those incase you have something obvious not right ?. Blank out any username / password.

I fixed the problem.
The port of POP3 was 110 using force usage of SSL/TLS security policy.
The port for SMTP was 25 using force usage of SSL/TLS security policy.
I changed the security policy on both to Use SSL/TLS on special port (legacy).
This changed POP3 port to 995 and SMTP to port 465.
I clicked refresh and I started receiving emails.

Ah ok, great you got your email working.

The port of POP3 was 110 using force usage of SSL/TLS security policy.
The port for SMTP was 25 using force usage of SSL/TLS security policy

Normally if you use POP3 port 110 and SMTP port 25 “you don’t use SSL/TLS” as they are not secure encrypted ports. So I suspect the mail server end had a glitch where it was allowing it to work anyway previously.