So do your correspondents not mind if they send to one address and get a reply from a different address? Not good for continuity.

I'd try the Folder Accounts add-on.

https://addons.mozilla.org/en-GB/thunderbird/addon/folder-account/

Your Thunderbird is acting exactly as it's designed to do.

It's not that they don't mind, they wouldn't care, but for some reason one of my recipients does not get my messages from a particular account (Yahoo). They bought an iPad and set up to receive emails on it from their usual account but for some reason they do not receive anything from Yahoo?? So to send to them I now use my gmail account, which they still receive (so far).

I will try your suggestion.

Ah, yes. Yahoo may well be on someone's spam blacklist again.

Maybe you need to help your correspondents to start using the preferred address (gmail?) when writing to you, then the messages wouldn't be in an inappropriate folder in your Thunderbird. But then I would have filed the messages between me and a friend in a folder set up just for that friend, rather than leaving the messages in folders connected to a specific account.

But I think Folder Account may help you. Another approach would be one of the identity-choosing add-ons, that supposedly examines who you're writing to and automatically selects an appropriate "from" address, or at the least, prompts you to check it. I've had mixed results with these.

It comes down to whether the identity you use to send is most usefully associated with a folder, or with an addressee. In my case, my interest was in avoiding using a personal account when communicating with business-related correspondents.

They can send to any of my email addresses but they do not receive my messages from Yahoo. She contacted her service provider and they went as far as to place me on their "good" list which made no difference. It seems to me that all her incoming messages are being scanned by a third party and my messages from Yahoo are intercepted?

I couldn't find a solution using folder accounts but will now try an identity-choosing add-on. Failing that I will have to train myself to ensure that when I send a message I choose the correct 'from' account.

Thunderbird is new to me and I'm learning. I went with Thunderbird because of this dilemma as I had no real reason to switch from my Yahoo account and use one of my others until now. As I still receive the majority of my correspondence in Yahoo, I needed a good email client which checked all my accounts. Switching accounts is a pain for most people.

I'm not sure if I solved this with one of the add-ons I installed but in settings I simply set the default identity email address for all my accounts to my gmail address (like duh).

Thanks for your help.

Oh darn! After testing this a bit further I found that I did NOT find a solution. Although my shaw.ca account did not care which return email address I used, Yahoo did and I received an error from their server when I tried to send this way. So I'm back to square one. As it stands now I must ensure that when composing a message I check to see that I have the correct 'from' email address chosen.

I have different accounts for different kinds of addressees (family, work colleagues etc.) so I need to be aware which account I'm using when I compose messages. I use the 'Account Colors' add-on which I find a helpful reminder.

The color solution may have worked but the Correct-Identity add-on worked (once I figured it out). I tested sending from all 3 of my accounts and the from address was the one I entered in Correct Identity. It took me a bit to find the window (correct identity options) which allowed me to set this up.

For those who want to know, get to the add-ons manager (Tools > Add-ons) and right-click on correct identity and select options. Once there, you can choose which identity to use with each account.