"Sending of the message failed.  The message could not be sent because connecting to Outgoing server (SMTP) smtpauth.earthlink.net failed. The server may be unavailable or is refusing SMTP connections. Please verify that your Outgoing server (SMTP) settings are correct and try again."
   Earthlink says (at https://clean.email/blog/email-settings/earthlink-email-settings) that for:
   SMTP (outgoing) the settings should be:  host=smtpauth.earthlink.net, port=587, security=STARTTLS, username=full email address including domain (as '[email protected]'), password=normal password; BUT NOWHERE DOES EARTHLINK PROVIDE INSTRUCTIONS ON AUTHENTICATION (whether 'no authentication' or 'normal password' or 'encrypted password' or 'Kerberos / GSSAPI' or 'NTLM') - I have tried "no authentication' and 'normal password' and 'encrypted password' - NONE of these options allows me to SEND my email out from Thunderbird.  **EARTHLINK needs to change ALL its instructions to clarify what authentication method will work - NOWHERE do I find any such instruction.**
   IMAP (incoming).  It was wonderful that after decades Earthlink FINALLY added IMAP (I've been with Earthlink since about 1985).  The above Earthlink website instructs to set Server IMAP settings to:  host=imap.earthlink.net; port=143; SSL=none; username=full email address (as in '[email protected]'); password=email account password.  Earthlink instructions on incoming IMAP security are unusual - 'none' is the default, but TLS is optional (but only if you set outgoing SMTP security to 'None'???)   My IMAP connection security is at the default 'none'.  Earthlink is silent on which [Thunderbird] IMAP authentication method to use ('password transmitted insecurely' or 'encrypted password' or Kerberos / GSSAPI' or 'NTLM' or 'TLS certificate' or 'OAuth2').  My [Thunderbird] authentication method is set to 'password transmitted insecurely'.
   BOTTOM LINE:   Despite my best efforts and Earthlink's muddy instructions, I cannot SEND email via Thunderbird to my Earthlink account servers and get the email delivered.  I always receive the error message above.
   PLEASE:  MOZILLA - Contact Earthlink and get this fixed.  I have written them a similar request to reach out to you, but please take the initiative - I REALLY would like this to work, as it once did.
   Thank you.                                                   5/3/2023

Using Win 10 (64) and Thunderbird 102.10.1 (32 bit), trying to send using Earthlink (IMAP) "Mindspring" email accounts ... I constantly receive this message: "Sending of the message failed. The message could not be sent because connecting to Outgoing server (SMTP) smtpauth.earthlink.net failed. The server may be unavailable or is refusing SMTP connections. Please verify that your Outgoing server (SMTP) settings are correct and try again." Earthlink says (at https://clean.email/blog/email-settings/earthlink-email-settings) that for: SMTP (outgoing) the settings should be: host=smtpauth.earthlink.net, port=587, security=STARTTLS, username=full email address including domain (as '[email protected]'), password=normal password; BUT NOWHERE DOES EARTHLINK PROVIDE INSTRUCTIONS ON AUTHENTICATION (whether 'no authentication' or 'normal password' or 'encrypted password' or 'Kerberos / GSSAPI' or 'NTLM') - I have tried "no authentication' and 'normal password' and 'encrypted password' - NONE of these options allows me to SEND my email out from Thunderbird. **EARTHLINK needs to change ALL its instructions to clarify what authentication method will work - NOWHERE do I find any such instruction.** IMAP (incoming). It was wonderful that after decades Earthlink FINALLY added IMAP (I've been with Earthlink since about 1985). The above Earthlink website instructs to set Server IMAP settings to: host=imap.earthlink.net; port=143; SSL=none; username=full email address (as in '[email protected]'); password=email account password. Earthlink instructions on incoming IMAP security are unusual - 'none' is the default, but TLS is optional (but only if you set outgoing SMTP security to 'None'???) My IMAP connection security is at the default 'none'. Earthlink is silent on which [Thunderbird] IMAP authentication method to use ('password transmitted insecurely' or 'encrypted password' or Kerberos / GSSAPI' or 'NTLM' or 'TLS certificate' or 'OAuth2'). My [Thunderbird] authentication method is set to 'password transmitted insecurely'. BOTTOM LINE: Despite my best efforts and Earthlink's muddy instructions, I cannot SEND email via Thunderbird to my Earthlink account servers and get the email delivered. I always receive the error message above. PLEASE: MOZILLA - Contact Earthlink and get this fixed. I have written them a similar request to reach out to you, but please take the initiative - I REALLY would like this to work, as it once did. Thank you. 5/3/2023