Dear Isaac,

I apologize for excluding you from the company holiday party I hosted last week. I neglected to update my personal directory and accidentally left you and several other recent hires off of the invite list. I assure you that the exclusion was not intentional and that I feel terrible about my mistake.

It is very important to me to be a team player in our workplace, and I typically make a point of reaching out to new employees and making them feel welcome. I am disappointed in my oversight and I regret any pain or stress I caused you. I have already added your contact information to my personal address book and I assure you that something like this will never happen again.

I sincerely ask for your forgiveness. I hope my mistake has not damaged our relationship and I look forward to getting you to know better at the next company gathering.

All the best,
Rachel