An error occurred in thunderbird "domain name required" 5.5.0

It appears Thunderbird is not looking in your address book.

emails are formed of 2 parts, the name and the domain. To make it clearer here is an example:

username@domain

e.g.

<email address hidden>

johnsmith = username
hotmail.com = domain

your group probably consists of a single word which is completely normal but as you can see from my example above, it will not have a domain name (also normal)

You could try browsing your address book groups rather than using Thunderbirds autocomplete-using-old-enties facility to make sure that it is referencing the custom groups you have created.

I would also log a bug to get this resolved

As another test, try creating a new test group and email that, it may only be affecting the groups from before the upgrade but new groups are ok. You need to work out what is ok and what isn't to get a grip on what is happening.

I don't personally use Thunderbird or any other mail client but I can certainly diagnose issues and advise.

Thanks so much for your insight. I tried a new list and had no problem. The idea of rebuilding these list is bad news as I have 500 names to sort and redo. Wasn't sure what you said about this part.
"You could try browsing your address book groups rather than using Thunderbirds autocomplete-using-old-enties facility to make sure that it is referencing the custom groups you have created." Thanks again.

Instead of typing the name of youur group, type hunting through the address book you have for the group using the mouse ad selecting the group that way, it may work.

Its good that new groups work, means the software is working and fine.

Let me know how you get on.

Got it! Thanks! Your answers got me probing and I found for some strange reason a double entry of my list, but the second entry wasn't in a use-able format. So cool how you all help, thanks!