Welcome to the admin side of the position. As with any promotion or higher rank there is always an increase in your own responsibility. As you move higher up the chain of command so the responsibilities increase too.
Some CO's may delegate additional responsibilities to you, but they will make these aware to you when you are taking on the position. These may be ship specific so it is best to discuss these with the CO.
However, as a DH on any ship you should be taking responsibility to welcome and greet your new junior officers. These may have been appointed to the ship by the CO, they might be recent academy graduates, or just an experienced role-player looking for some fun. Whatever the case always send them an email welcoming them to the ship and saying who you are.
It helps to create a good atmosphere and gives that person a link to the ship and the crew. This is especially important if the person is new or just starting out. Remember, we were all there once!!!
What is a welcome email? Simple, it is an email that you send welcoming someone in your department to the ship. Be friendly, give them some details, and maybe even provide a sim update or a potential starting pointer. Help the person out.
On many ships the CO and XO send out their own welcome emails, but there is no excuse for you not to add your own personal touch. Remember, people like to deal with people and we are all here to have fun!