Mar 11, 2019 — This no longer works like this.
Many people are confused about the difference between starting a tweet with @someone vs. .@someone, i.e. adding a dot or a period before the username.
Here’s the difference:
If you just reply with @username the tweet will only go to people who follow both you AND that person
If you add a dot before the username, it’ll go to all of your followers
So, by default, when you reply to someone, most of your followers won’t see what you said to that person unless they also follow the person you replied to.
If you want all your followers to see what you said to them, add the dot before the handle.
Actually, adding anything before the @username will cause the tweet to go out to all your followers. Adding a period is just an easy way to do it.