To auto-tweet a link to your newsletter’s archive, first connect your TinyLetter account to your Twitter account. (Only one Twitter account can be connected at a time to use with the auto-tweet setting.) To connect your accounts, go to Username > Your Profile, and click on Connect With Twitter under the Twitter account option. This will take you to Twitter's login page, where you’ll provide your Twitter login credentials and authorize the connection.
Once your Twitter account has been authorized, go to Username > Your Profile and enable the auto-tweet setting. You'll see the Twitter account that’s connected. Select the checkbox for Auto-tweet new public letters to apply the auto-tweet setting for all future newsletters you send.
Finally, you need to make sure public archives are enabled for your account. (We won’t auto-tweet letters that aren’t public.) To do that, scroll down to the bottom of the Your Profile page, select the checkbox next to Show sent messages on your archive page, and click Save Profile.