Thunderbird does not limit how many emails you can send. It is just a program on your computer. However, your email provider can place limitations on number of emails sent via their server. This may be number of emails in any given period eg: per hour or in any 24 hour period. Or perhaps they have a limit on size/bandwidth. * http://kb.mozillazine.org/Limits_%28Thunderbird%29 ''There appears to be a limit of approximately 60 addresses when sending messages if you manually 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.'' This is usually the case if you are sending one email to several email addresses and emails are sent uisng Bcc. ''You can receive messages sent to multiple addresses in the same mailbox. Any limitations would be due to your e-mail provider. '' If you are looking for a way of sending a more personalised email to several people you can use 'Mail Merge' addon. This uses the 'To' field and sends one email to each individual email address. You create a template email in Thunderbird, Mail Merge hooks that template up with eg: .csv file to insert personalised data held in Column headers. You can have them send using 'Send Later' option to put them in the 'Outbox' so they can be double checked before sending. https://addons.thunderbird.net/en-US/thunderbird/addon/mail-merge/ It would be useful to check what other software is being used, such as Anti-Virus scanning of outgoing mail as it may be slowing down the process. Are the emails completed created in Thunderbird using templates etc or are you using other software like MS Office 'Mailto' process/ Send to mail recipient which then uses Thunderbird? What version of Thunderbird are you using? Is it '''52.9.1''' or '''60''' or another ?