Are any of the accounts with googlemail?

If you use the googlemail smtp server to send, it will insert the associated googlemail address into sent messages. Some solutions open to you are:

1. Set up specific googlemail smtp "accounts", one for each "from:" address.
2. Register any non-googlemail addresses with the googlemail account, allowing them to be used as "from:" addresses. If you do this, it may be convenient to set up the preferred address as an additional identity in Thunderbird.
3. Find an alternative non-googlemail smtp server; maybe one offered by your ISP or email provider.

Over and above all this, do check in Thunderbird that it has offered an appropriate From: address. It will default to using whatever account you happen to have open at the time you create a new message. The available From: addresses are offered in a drop-down box at the top of the form in which you write a message, though the googlemail smtp server will ignore this, and silently insert its own address.

If it is a simple matter of you forgetting to check the From: address, there are many add-ons available to help with this, from a simple one with colour coding which forces you to make a choice, to more complex types that analyse the message to which you're replying. I find these latter types are not quite as effective when starting a new email messages, as opposed to forwarding or replying.

thanks for your reply. I do check that I have the right from address at the top when I'm sending but perhaps I will have to ensure that I have the right inbox open as well. there are separate smtp accounts for each gmail address with one marked as default. I have tried to remove the default tag as I thought this might be causing the problem but TB won't let me do that