em Client On Yahoo mail account I consistently get "Unexpected end of stream" authentication errors.

Two different laptops with two different Yahoo mail accounts.  Sometimes works OK, but many times I get -  authentication error - Unexpected end of stream.  Then wont send or receive. Happens on both machines.

I have this issue with Yahoo too.

I also have this issue frequently, but not only with emClient. It also happens with Outlook.But since I use my Yahoo account mainly as waste paper basket for ads and other spam, I don’t care much.

Maybe it’s a problem on the Yahoo side?

It is most likely a Yahoo issue. You could contact them and ask.

Authentication issues may be caused by either incorrect credentials or incorrect settings. To check the settings are correct, go to Menu > Tools > Accounts and check you have the correct combination of port and security policy.

Port 587 = Force usage of SSL/TLS
Port 25 = Use SSL/TLS if available
Port 465 = Use SSL/TLS on special port (legacy)

Port 993 = Use SSL/TLS on special port (legacy)
Port 143 = Use SSL/TLS if available

Port 995 = Use SSL/TLS on special port (legacy)
Port 110 = Use SSL/TLS if available

These are the correct combinations of port and security policy. The underlined ones are the best option for security if your server supports them. SMTP port 465 was reassigned and should no longer be used for SMTP, though many mail providers still recommend and use it.

Is port 587 for smtp only good for Yahoo mail? Can it be used for Cox?