When do I need to send a thank you letter/email?

You should send a thank you letter after an informal or formal interview, company visit, or other career exploration activity. In addition, we recommend sending a thank you letter when someoneprovides you with job search assistance such as referring you to an employer, providing a network provides you with job search assistance such as referring you to an employer, providing a network contact, or speaking on your behalf to a prospective employer. Bottom line, when in doubt - send a thank you letter there is nothing wrong with being over courteous.