The following info explains why you are having an issue. Information also offers a way of allowing you to continue with your elaborate way of doings things. In addition, I've also included two other means of achieving the same result, but with less hassle. It is not the best idea to copy paste anything from any Word Processing Program. This is because Word Processing programs use a lot more formatting options because they are designed to create documents not emails. This means when you copy paste eg: an MSWord document into something that uses HTML, you are not just copying text, you are also copy pasting a whole load of extraneous and unnecessary coding. This causes your emails to become bloated and much larger than necessary. It may also effect what the recipient actually sees. Not everyone may have the fonts you have chosen to use etc. The issue of extra lines etc is probably you seeing some of the effects of hidden css coding that you are importing into that email. I've had emails that have hardcoded css so that when I want to reply, I'm forced to use the same css coding and not what I wish to use, so I've had to locate the emails in my profile and rewrite the coding...not very helpful. So if you are doing this unnecessary method of copy pasting, please use: * 'Edit' > 'Paste without Formatting'. re: ''contents of the e-mail are almost entirely the same'' Why are you not using the function available in Thunderbird? Click on 'Write' Type the standard email and save it as a Template email in Templates folder. Then when you wan to use it, select 'Templates folder and double click on the email to open in a 'Write' window. You can then edit as required and send out. This will save all the unecessary timewasting of copy pasting. '''RE: 'Mailing Lists' and 'Template' email'.''' Are you aware of the following two methods: '''1)''' Create a 'Mailing List' in Thunderbird and send out one email to a group of people using a premade Template email which can be edited as required prior to sending. You can use Bcc to hide recipient email address, although it is advised that at least one email address uses a TO field even if it is your own. More info here: * https://support.mozilla.org/en-US/kb/how-create-and-use-mailing-lists-thunderbird '''2) '''Use a *.csv file or Thunderbird address book with a Thunderbird Template email and an addon extension called 'Mail Merge' to create personalised emails that can be created and sent with minimal input. Each email uses the 'TO' field one email per person and can be used in a 'SendLater' mode which puts emails in 'Outbox' allowing you time to double check prior to sending out in one go. https://addons.mozilla.org/en-US/thunderbird/addon/mail-merge/ Images below as aid. shows a simple template email, although you would also include content. Simple excel *.csv file showing column headers that match those used in Template email. Additional images showing options that use .csv file or address in Thunderbird. Note a *.csv file can be imported into thunderbird to create as address book.