You would have to check your server settings for that account.

you would need to post information showing what server settings you are currently using. Menu icon > Help > More TRoubleshooting Information Under 'Mail and News Accounts section. Copy all the data and post the information into this forum question OR Post images showing: Account Settings > Server Settings for incoming Account Settings > Outgoing Server (SMTP) > select account/email address Post image showing settings

But I believe these are the settings you should be using.

Earthlink.net (EarthLink) IMAP Server

• Server name: imap.earthlink.net
• port 143
• Connection SEcurity: none
• Username Your full email address
• Authentication Method: Normal Password
• password Your Earthlink.net password

Earthlink.net (EarthLink) POP Server

• Server Name: pop.earthlink.net
• port 110
• Connection SEcurity: none
• Username Your full email address
• Authentication Method: Normal Password
• password Your Earthlink.net password

Earthlink.net (EarthLink) SMTP Server

• Server name: smtpauth.earthlink.net
• port 587
• Connection Security: STARTTLS
• Username Your full email address
• Authentication Method: Normal Password
• password Your Earthlink.net password

To use the above insecure settings - You may discover the 'Authentication Method' for incoming and outgoing may need to be 'Password, transmitted insecurely'

It seems some sites report you can use a secure setting, so use a secure setting rather than the original default insecure settings I previously mentioned.

Earthlink.net (EarthLink) IMAP Server

• Server name: imap.earthlink.net
• port 993
• Connection SEcurity: SSL/TLS
• Username Your full email address
• Authentication Method: Normal Password
• password Your Earthlink.net password

Earthlink.net (EarthLink) POP Server

• Server Name: pop.earthlink.net
• port 993
• Connection SEcurity: SSL/TLS
• Username Your full email address
• Authentication Method: Normal Password
• password Your Earthlink.net password

So really it is important to know what settings you are currently using in order to know what part is currently not being accepted.