Adding a clear and meaningful subject line to your messages is crucial. It will give your recipient a good idea of what your mail is all about.
And in addition to being straight and to the point, also try to keep it as short as you possibly can.
Email clients can only display a limited number of characters for the subject in the mailbox display. Although this depends on the user’s settings, you can safely assume that about 40-60 characters can be displayed in just about any email client.
Overly long subject lines not only get cut off by the email client. They also puzzle the recipient, who expected a short and snappy summary, and not the full content of your message crammed into in the subject line.
Conclusion: Make up short and relevant subject lines. They’ll tickle the recipient to open your message, read it and respond.