http://kb.mozillazine.org/Limits_%28Thunderbird%29#E-mail_addresses

"There appears to be a limit of approximately 60 addresses when sending messages if you enter each address separately."

This doesn't appear to me true. I finally decided to run a test with separate addresses and found I was able to send to 200 individual recipients in one group email.

I'm puzzled by your choice of words.

• 200 individual recipients
• one group email

What is a "group email"?

A group email? Just an email to multiple recipients. to a group rather than to a single individual. Does my previous reply still not make sense?

"My ISP says it doesn't impose a limit on the number of recipients" What ISP please.

And the exact text of the error message (Verbatim)

OK, so it was one email message with many discrete addressees. Often, users say "group" referring to features found in Outlook, similar to Mailing Lists in Thunderbird. Given that "group" can have such a specific connotation, it's useful to know exactly how you are using it.

The limit mentioned in my link is a bit mysterious. You'll notice it says "appears" and "approximately" as if it's an empirical discovery rather than by intimate knowledge of the underlying code. My guess is that there is a fixed-size buffer allocated to storing addresses which will only hold so many characters. Maybe this theory is incorrect. Maybe the buffer got bigger. :-S

What we do know is that Mailing Lists are successful where Thunderbird does complain about too many addresses.

It's HIGHLY unlikely the reason my test email limit turned out to be 200 recipients because of a fixed-size buffer that just happened to coincide with that number. Much more likely they just say "approximately 60" in their help file notes to discourage spamming.

Well, no, because 4 or 5 times a year, someone writes in with pretty much exactly your question because they too have had a message refused with the "too many recipients" warning. We suggest they use a Mailing List and all is well.