Read section 'E-mail addresses':

• http://kb.mozillazine.org/Limits_%28Thunderbird%29

When sending one email to a large number of email addresses, it is better to create a 'Mailing list'.

• http://kb.mozillazine.org/Thunderbird_:_FAQs_:_Create_Mailing_List#Create_a_new_mailing_list

• click on 'Address book'

Create a mailing list which will look like a sub list to an address book. The email addresses need to be in the top level address book and the contact must have a valid email adress.

• File > New > Mailing List
• under 'Add to:' choose the main Address Book
• under 'List Name' - give it a name.

In my example shown in attached images, I called it 'Test'. you could enter the email addresses one by one in the list area, but there is a much quicker way.

• Click on OK to close window and create the Mailing List.

Now to add the email addresses.

• select the main address book
• highlight all the contacts you want in the Mailing List.
• then left click and hold down and drag the contacts into the list which is a sub list to that address book.

see first image. Personal Address Book is the top level address book and Test is the Mailing List.

Then you aready to use the Mailing List. There are two methods, choose whichever method is best for the situation.

Method 1:

• Open a new Write message.
• Make sure the Contact Sidebar is visible
• View > Contact Sidebar
• Select the top level address book
• Look in the list of contacts for the Mailing List name.
• Select and click on 'Addto Bcc' or other option.

see second image. It will enter the name of the Mailing List - not the individual names. You cannot edit the list via this method.

If you really want to see all the indiviual names, so that you can edit the list then you need to use a slightly different method.

Method 2:

• In Address Book
• Select the Mailing List.
• Click on 'Write'

This will enter each individual name in it's own TO field. At this point you can choose to change the TO option to Bcc, but it is a bit long winded, which is why I showed you the first option to enter the whole list as Bcc. You can also edit the list - maybe to remove someone.

Remember, which ever method you use, it is always a good idea to include at least one name in a TO field. such as your own email address if you do not want to disclose all your contacts email addresses. Some servers can think it may be spam if there is nothing in a TO field.

While the above reply gives you an exact answer and really all you need ... there is likely another bottleneck: Providers/ISP (even if you have your own hosting provider) have their SMTP limits.

In my experience some have lowered this limit to 50 (or even fewer) emails per message or even per hour. Of course the risk of sending out spam (unwittingly) is the reason.

You may chech with your ISP before running into this problem, asking for an SMTP or E-Mail Sending Limit.