Welcome letter is used to enhance the relationship between an employor and his new hire, just after the applicant accepts the job offer and before he starts working at the company. The welcome letter can take many forms and it can serve many purpose, but its main purpose is to encourage, to excite and motivate the new guy (or girl, depending the case – but I’ll consider as “him” for now) to start working in the new environment and having the best performance. On the other hand, a bad written letter can discourage him and make him nervous about his new position.
The welcome letter should make the new hire to understand that he is welcome because he earned his position, it should give hime some standards about what he must expect in the future.