I don't have that any longer, and I think it's because of one of my add-ons.

The Identity Chooser add-on allows you to colour-code accounts and warn you against using some of them. In my case here at work I have a few personal addresses that I rarely use and I don't want them popping up as "from:" options. OTOH, I don't want to remove these accounts either.

This add-on allows a pared-down list of preferred accounts to be offered, and in doing this it seems to inhibit the "customize address" option.

https://addons.mozilla.org/en-US/thunderbird/addon/identity-chooser

I appreciate that this is not a good solution. You would really want to disable this feature by default, rather than have it there and somehow configure Thunderbird to disable it.

I'm not sure why this feature was introduced. I know there is a small number of users who are able to generate "throw-away" addresses and this feature is useful to them in particular, but it isn't helpful to the vast majority of users.

However, in many cases, you couldn't use the feature, because most email providers now forbid the use of arbitrary "from:" addresses.

Have you actually tried to send a message using another person's email address? Does your server let you do this?

When I configure gmail to Thunderbird, it is automatically disabled in PoP. So you are right that should be blocked of service provider. But I have another third party email application provider which does not have any feature as default. so whatever needs to be done, seems to be done through Thunderbird only either by add-in a other wise . Kindly suggest .

Do you think, thing could be done through config editor?

Thanks in anticipation.

As per suggest by you , I have tried with your add -on . but it is showing some error . kindly check attachment ,

Problem solved out . Thanks your support ..........

thank you very much .