is there an easy way to copy all adresses from a group to use them in third party software (e.g. Thunderbird, Word, Excel)?

In detail one customer writes an email to a bunch of internal and also external addresses. Now he wants to mark all "To" entries and save the emailadresses of them to a file.
My first idea was it to create a group out of this recipients and then export the address book. Unfortunately in this case are all informations included and he just wants the emailaddress...

Any suggetions?