This is an error at the server end. perhaps you need to check that all of the email addresses are entered as all lower case.

If your provider is Yahoo (so ATT, BT?, AOL, Verizon or one of their other many cotract jobs), then it would appear they also use the code when they think amessage is spam.

Given you offer nothing about your setup or provider, that is about all I can suggest. But if you are sending to mailing lists, it might be the number of mails sent in a short time. Especially if you are sending to a number of lists. (it may be not the 10 that is an issue, it might be the 51 in 30 minutes or something like that. Or it might be your provider is not limiting you to a maximum of 10 emails in a period of time.

Thank you Matt, for your help. Will try to use all lower case. It worked before for almost 3 years with no problems and since than i havent change anything. Lets hope the lower case will fix the problem.

Hi Matt, so i tried to do what you said, it didnt work. Now its saying Failed due to unexpected error 80004005. And still showing the same error before.

re: group emails

Are you using a 'Mailing List' or entering email addresses separately ?

Is each email address entered in it's own line or are they all written on the same line separated by a comma or semi-colon?

Is each email address in a 'Bcc' field ?

TEST: If each email address is entered on it's own line and set as Bcc, please add one email address in a 'TO' field, even if that email address is your own. Please post result of test.

Thank you for responding so quickly. Yes its separated by a comma as cvs file.

I send one template to a group of emails which are uploaded in the form of CSV file

In the csv file, if you open and read using eg: MSExcel, are there any empty lines?

In other words, are the contact details written on one line after the other with no spaces between each contact. If there are any empty lines, please remove them and save the file.

No empty lines. Do you think i have problems because a lot of people using the program now?

If you are sending a load of emails then it is better to use a 'Mailing List'. This means importing the .csv file to create as an address book, then creating Mailing List.

• https://support.mozilla.org/en-US/kb/how-create-and-use-mailing-lists-thunderbird

There are limits on number of emails that can be sent. http://kb.mozillazine.org/Limits_-_Thunderbird#E-mail_addresses

Alternatively, use the addon called 'Mail Merge'. Then you can create a template, save in 'Templates' folder . select template edit any required content and use Mail Merge to use .csv file or specified address book to create the emails as individual emails and each uses a TO field. You can put use 'Send Later option to store in 'Outbox' so you can check contents and send when convenient.

https://addons.thunderbird.net/en-US/thunderbird/addon/mail-merge/

images below as guide, but addon link also shows helpful images.

Thank you so so much. Will do that! I really appreciate your time and help.