Gmail Priority Inbox – Send Mail Marked as Priority

You can’t control if a message will be marked as important in the recipient’s inbox. The priority marks in Gmail are algorithm-determined so you can’t control them.

How importance ranking works

To predict which of your incoming messages are important, Gmail automatically takes into account a number of signals, including:

• Who you email: If you email Bob a lot, it’s likely that messages from Bob are important.
• Which messages you open: Messages you open are likely to be more important than those you skip over.
• What keywords spark your interest: If you always read messages about soccer, a new message that contains those same soccer words is more likely to be important.
• Which messages you reply to: If you always reply to messages from your mom, messages she sends are likely to be important.
• Your recent use of stars, archive and delete: Messages you star are probably more important than messages you archive without opening.

See this help page for more details.