the best method would be to use Mailing lists. See info here: https://support.mozilla.org/en-US/kb/how-create-and-use-mailing-lists-thunderbird

There appears to be a limit of approximately 60 addresses when sending messages if you enter each address separately. However, if you use Mailing Lists (mail distribution lists) for most of the addresses any limit is imposed by whatever SMTP server you use.

brisboy1998 said

I wish to use Thunderbird as the email program for our boat club with 170 members. We send out an update to all members once a week, but Thunderbird will not send this number in one batch. If this is not possible, how can I divide the email addresses into groups acceptable to Thunderbird?

Thanks for your help Toad-Hall. I'm sure this will solve the problem.