email: error message is "(after RCPT TO): 550 authentication required"

[SylvanOgre]

This suddenly happened this week.
I cannot send email to any of my oc***.x10host.com email addresses. The sending address gets a "mail delivery failure" with the following:

This message was created automatically by the mail system (ecelerity).

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

>>> ra***@oc***.x10host.com (after RCPT TO): 550 authentication required

I have been using the x10host emails for several years, and suddenly this week I start getting these bounce backs.

NOTE: I can SEND from x10host.com, I cannot RECEIVE to x10host.com.
I tried with both x12.x10host.com and with mail.oc***.x10host.com, and both give the same failure.
What is this sudden authentication requirement, when last week (and the last several years before that) I can receive emails on all of my x10.com email accounts?

 

[mrburnsx]

Please try following the instructions in https://community.x10hosting.com/threads/x15-email-issues.210984/

If the box "Use this server to handle my e-mails. If not, change the MX records and uncheck this option," is already checked, uncheck it and click save, and then recheck the button and click save.