I think your SMTP entry for that account is perhaps actually set to AOL.

Tools menu (alt+T) > account settings > click on the account name and confirm the correct SMTP server association in the SMTP drop down.

The outgoing mail server for the Yahoo account is the default (Verizon) mail server. This is what's recommended, or at least that's what's worked for the past 8 years or so. Changing it to the AOL server might make it possible for me to send mail to myself from the Verizon to the AOL accounts (or maybe not - I haven't tried it) but I'd rather not make another problem when solving this one.

The outgoing servier for the AOL account is the AOL server, which makes it possible to send mail from one of my AOL accounts to another, and send mail to the Yahoo and Verizon accounts that looks like it's actually coming from AOL, so this appears to be the right way to do it.

I believe that the problem is that AOL sees a message (apparently) from a Yahoo user that's coming from a Verizon mail server and not a Yahoo mail server. .

Your belief is 100% correct. Verizon used to block port 25, but your should be able to use the correct yahoo server these days as it is on Port 465 and uses SSL. Server is smtp.mail.yahoo.com Username your full yahoo email address.

per https://autoconfig.thunderbird.net/v1.1/yahoo.com

I'm pretty sure I tried that before but I tried it again, this time taking a closer look. I checked in the Options/Security/Saved Passwordds window and the user name and password for Yahoo are correct there. However, when I open the Account Settings and select Yahoo from the SMTP outgoing servier pulldown list, it doesn't stick. I click OK, close the window, and the next time I look at the Account Settings for the Yahoo account, it has returned to using the Verizon server (which is the default).

Is there another step that I'm missing here? Seems like it should work, but it doesn't. I remember that a couple of years ago when I was trying to get this to work and eventually gave up, there was a fairly complicated method of making a specific account use a different server.

The version of Thunderbird that I'm currently running is 24.6.0

Never mind

OK, it's all my fault. I was looking in the wrong place for the outgoing SMTP server. Apparentlyl I was looking at the default setup rather than the setup for an individual account. I figure this is from some old advice with a much earlier version of Thunderbird, which recommended using the same SMTP server for every account, and what I was looking at was the default SMTP servier, which, of course is why selecting another one didn't "stick" since I didn't make it the default. Apparently Thunderbird has now accommodated the fact that you can no longer get away with using the same SMTP server and provides an entry for each e-mail account. EUREKA

I can now send mail to AOL and G-mail using Yahoo via Thunderbird.

I have another problem with configuring Thunderbird for a G-Mail account (it says it can't verify the user name and password, which I know are correct), but I'll look for a solution for that before I whine too much.

Thanks for putting up with my ignorance, or rather, lack of observation. .

Suddenly, all a-mail addressed to recipients with AOL e-mail addresses are being rejected if I compose and send from Thunderbird, but if I send the same message to the same recipients directly from my gmail account, they go through with no issues. These accounts worked perfectly until the middle of last week. HELP!

Check the Account Settings for your AOL setup in Thunderbird and make sure that the Outgoing Server is smtp.aol.com. That fixed the identical problem for me.

You get there from the Tools/Account Settings menu, then select the AOL mail account. The outgoing server is the last thing on that page.

Guess there is some confusion concerning my post . . . I have a g-mail account and am using Thunderbird as my mail client. If I send an e-mail TO an AOL account using Thunderbird to access my g-mail account, they are bounced by the RECIPIENT's aol. I am not using AOL. Sorry.

This is why it is best to start your own thread with your details and not hijack someone else's thread. You get a more accurate answer.

What is the error you get back with the returned message?

Technical details of permanent failure: Google tried to deliver your message, but it was rejected by the server for the recipient domain aol.com by mailin-04.mx.aol.com. [64.12.88.132].

The error that the other server returned was: 521 5.2.1 : (HVU:B2) http://postmaster.info.aol.com/errors/554hvub2.html

I do not know why providers bother adding these error codes and resolution hints. No one reads them.

554 HVU:B2

   There is at least one URL or domain in your e-mail that is generating substantial complaints from AOL members. Resolution will require opening a support request.

Most error codes that I am familiar with are relatively specific, and "554 HVU:B2" is not the same as "521 5.2.1 (HVU:B2)" from what I knew. Additionally, the issue appears to only happen when using Thunderbird as my mail client . . . If I go directly to my g-mail account, all works well. To me, this points to Thunderbird as the issue. I've been wrong before, but something doesn't seem to fit. Not trying to be argumentative, but if eliminating The client eliminates the issue, logic tells me the issue is with the client. I've been wrong before . . .

So are you using Thunderbird to send mail as a Gmail user to an AOL user? In that case, make sure that your Gmail setup in Thunderbird is using the Gmail outgoing mail server.

Another thing about Gmail is that they have a "2 step" authentication. Thunderbird doesn't deal with that very well, or at least didn't when I had a problem with it. You can go into your GMail settings and turn it off.

got a signature in Thunderbird that is not on your gmail server. I think you might have.