I am a brand new Verizon customer and got this Authentication error too. I followed the link to the Verizon notification and set my Outlook Settings accordingly and it worked. Here are screen shots of my Outlook 2010 settings. The second and third shots appear after clicking on the Advanced Settings button:
Has anyone had (and hopefully solved) this problem lately? My mother uses Eudora as her email client. A few days ago she started getting the "550 5.7.1 Authentication Required" error when sending mail; she has been using smtp.verizon.net port 465 all along and hasn't changed anything. She can still send email from the web interface and also from her iPod. A phone call to Verizon support was not helpful.
I have had the same issue since August 01, 2014. Verizon tech support is no help. They are sending me a new router which I doubt will help.
I took my laptop which shares the same issue with my desktop to an friend with FIOS on NYC and the issue goes away. I come back home & it is still here.
I am guessing a local server issue.which Verizon seems to deny.
New router tomorrow & we will see.
Identical issue here that started Aug 1, 2014 using Eudora as the mail client. It happens both on a Rogers (Canada) USB stick while I was away over the weekend and also from the DSL connection at home. Sending from my iPod is OK so is something that is unique to Eudora, though it continues to work fine with other email accounts I have through other providers. Based on comments already here I am not going to try to call tech support. Very frustrating, especially since this follows Verizon's shutdown of person web pages, which was part of my original Internet contract. VZ doesn't seem to want to please its customers, it seems.
I installed Thunderbird on my laptop today and from the imported settings from Eudora I can send with no issues through my Verizon email accounts. So whatever Verizon changed on 8/1/14 caused it to not work with Eudora any more but is OK in some other email clients like the iPod and Thunderbird. What is really bizarre about this is I had the T-bird install import the server settings from Eudora -- I touched nothing in those settings! -- and it works fine from T-bird.
Weird, and frustrating. I have tens of thousands of emails in Eudora and T-bird doesn't seem to want to import the emails without a few machinations.
Later Edit: Just saw your post that you were able to resolve the issue after finding one of the (many) threads on this issue. I decided to leave the rest of this post as-is in case it helps someone else...'-}}
There are a number of threads discussing this issue and most of the threads have the solution.
Find the eudora.ini file (should be in the folder where Eudora is installed)--some have a deudora.ini file--and using something like Notepad, edit the eudora.ini file adding the following line in the [Settings] section--save the file after making the change:
See the thread "Problems sending email..."
For mac-side Eudora users, take a look that thread "Eudora & mac-side solution..."