It is customary at this time of the year to say sorry to people and to ask for forgiveness for anything you might have done to intentionally or unintentionally hurt someone.
I found this interesting question and answer that has relevance here:
From: E. T. in Denver
Is it permissible to ask for mechila (forgiveness) over an email network rather than in person? I know it's not preferable, but many of us work in large networked environments. We considered the option of sending it receipt-requested to a specific address rather than an all-points broadcast. Thanks!
Dear E. T.
There are two components in achieving forgiveness from someone we have wronged. One is the initiative of asking for forgiveness; the other is the granting of the forgiveness. Ideally, we try for both. While doing so in person is the best way to appease someone, it is not always possible. Asking for forgiveness in a written letter, over the phone or in cyber space is also acceptable particularly when the person responds. Nevertheless, even if a person doesnt confirm his forgiveness, in the pre-Kol Nidre confession a Jew says that he forgives anyone who wronged him, and prays that Heaven will inspire others to forgive him as well.
That being the case, "I'm sorry"!