We need some more information, who are your email-service provider. Apparently you get a answer from your mail-server about some recipients. Are they all on the same server? Some providers set up filters to stop spam and just allow a certain number of emails in a spec time-frame from one IP.

It could also be some typo, look for an extra , in the address before the faulty ones. I don't know any limits on Tbird. from http://kb.mozillazine.org/Limits_-_Thunderbird

" E-mail addresses

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

You can receive messages sent to multiple addresses in the same mailbox. Any limitations would be due to your e-mail provider. "

bdbinatl said

Sometimes when I try to reply all to a message with 10 to 15 recipients on it, I get an error message that says: An error occurred while sending mail. The mail server responded: Requested action not taken: mailbox unavailable Failure sending mail. Try again later. Please check the message recipient <some recipient> If I remove the name from the list of addressees, then I get the same error message with another recipient. If I delete them, then it happens again with another. Is there some limit to the number of addresses one can sent a message to? If so, is there a way to increase that limit?

My email is with gmail. There are no extra commas. The first error is reported on a yahoo account. After I delete it from the reply list, the next one is a hotmail account. The one after that is a bellsouth address.

what I now Gmail has a limit on private mail accounts, I think its a hundred /24 hours or if there are many bouncing mails. (In the name of stopping spam) They have a business account that don't have that limit. (spam allowed?)

bdbinatl said

Sometimes when I try to reply all to a message with 10 to 15 recipients on it, I get an error message that says: An error occurred while sending mail. The mail server responded: Requested action not taken: mailbox unavailable Failure sending mail. Try again later. Please check the message recipient <some recipient> If I remove the name from the list of addressees, then I get the same error message with another recipient. If I delete them, then it happens again with another. Is there some limit to the number of addresses one can sent a message to? If so, is there a way to increase that limit?

I just tried sending again, first thing in the morning and got the following error message:

An error occurred while sending mail. The mail server responded: Requested mail action not taken: mailbox unavailable Too many recipients. Please check the message recipient #####@aol.com and try again.

Notice that the main problem seems to be too many recipients. 16 is too many recipients?????

So, I decided that since I was getting the error on a Reply All operation, I would create a new message to all 16 recipients and try sending it. I got almost the same error message, but this time "too many recipients" was replaced by "mailbox unavailable". I tried removing the addressee and sending again and got the same error message. And did so for the next 5 people I removed. At this point, I think I'm going to download Eudora . . .

The error message is coming from your email providers server. I am not sure what you think Thunderbird has to do with it other than deliver the message to you.

bdbinatl said

Sometimes when I try to reply all to a message with 10 to 15 recipients on it, I get an error message that says: An error occurred while sending mail. The mail server responded: Requested action not taken: mailbox unavailable Failure sending mail. Try again later. Please check the message recipient <some recipient> If I remove the name from the list of addressees, then I get the same error message with another recipient. If I delete them, then it happens again with another. Is there some limit to the number of addresses one can sent a message to? If so, is there a way to increase that limit?

An update: I tried doing a reply all on my message using two other email applications I downloaded and configured and got the exact same error message on them, so it has to be something with the recipients addresses. I noticed that some have a direct email address and others have a persons name and email address, so maybe this has something to do with it. At this point, I say close this problem report. Thanks for all the suggestions!