Ive been getting this problem as well thankfully this post has fixed my issue glad to see it wasnt something on my end but on yahoo’s end woot woot
Hi Dalton, glad this helped you to resolve the issue, but just to let you know, Yahoo just changed some of it’s settings recently again, and even though changing the settings as instructed here is still correct, you might be seeing this error again if you’re using Contacts/Calendars on your account.
To avoid seeing the unauthorized popup go to Tools > Accounts > Your Yahoo account, and change the CalDAV and CardDAV address under Contacts and Calendars tab from:
…/users/[email protected]/ to …/users/yourusername/ , just change the end part to not contain the @yahoo.com part as well and everything should work properly.
Hope this helps,
Paul.
I’m having the same issue (version 6) but my account is a hotmail.com account. I tried following the disable calendar and deleting the domain tricks. Doesn’t work. Same screenshot but asks for password for Airsync. 
Please help ASAP! ANYONE!
Hi Nahian,
if you are experiencing a problem with AirSync, I suggest setting up your hotmail account as IMAP.
Just choose the Mail>Other option in the New Account setup and input outlook incoming and outgoing mail servers manually.
regards,
Olivia
Hello,
I am also still receiving the above error and have not been able to receive any incoming mail. I do not use Yahoo either. I know my password is correct and when clicking on the errors tab same thing - could be caused by temp server unavailability or incorrect settings - everytime auth failed
Hi Cyndi,
can you try adding eM Client to the exceptions in your Windows Firewall and Antivirus software and see if the issue persists?
Regards,
Olivia
I thank everyone for all their comments and comments to resolve my issues.
But, I am visiting my parents out of town and am unable to access emclient.
Will definitely try when I return home. thank you for your response
Holy great tip, batman. It worked.
I am getting the SAME message ad I don’t even use email or contacts in eMclient. I only use it to view an iCloud calendar. As of now I tried unistalling and reinstalling and now i have NO calendar because I can’t get anything to reload.
Hello there I am having an issue logging into my emclient email Is it possible to reset my password on my eMclient account I am unable to sign in and would like to send emails I have forgotten my username too so if you can help me out I`d appreciate it
Hello dougd17323,
If you wish to reset the password to the email account, you need to do it directly at your server provider’s page.
Russel