In an email before the start of the course, you as the teacher can show an awareness of the situation of digitization and the lack of social proximity. It is also a good idea to tell the students what you think about the situation (online teaching and learning). You could also adress your feeling of speaking into an empty room and make a plea for creating as much vividness as possible together in the course (ask the students to leave the cameras on and to participate actively).
As an alternative to a welcome email, send your students an introductory video before the start of the course. In this video, you could introduce yourself as well as your wishes and expectations for the course. This creates a stronger personal connection than an email, but is also more time-consuming.

„Taking time to get to know each other is (…) essential for ‘warming up’, and is vital in the online setting“ (de Nooujer/Schneider/Verstegen 2020, o.S.)..[1] It therefore makes sense to promote contact between students even before the event; e.g. with a hall of fame or the "I-marketplace": in the forum, everyone should introduce themselves with three pieces of information (or pictures).
In a more interactive variant, the students could place a wrong piece of information in their introduction - and the other students guess together in small groups (via a conference tool, group rooms, so-called "breakout rooms" can be set up) in the first session which piece of information is probably wrong.
Often, pictures can be integrated into the forum, so that this presentation can also be implemented - instead of in text form - exclusively through pictures. These do not have to be photos of the person, but e.g. photos, which refer to hobbies or interests.
Such a visual introduction is not very time-consuming, but produces curiosity and is thus well suited as a preparation for getting into conversation in small groups during the first session.

Digital competencies should not just be expected. Explain to your students how to get into the course and where they can find relevant information:

• Send a message to all members of the your course indicating where important information such as the link to the meeting room can be found in the future.
• Store important information about the event in your course on the learning management system.

By asking the students (e.g. in a short online survey) what is important for them for the course, what they want and expect, you signal that a dialogical learning culture is important to you and that the students have the opportunity to participate in the planning and design of the event. At the same time, however, this also means - and you should also make this clear - that you share the responsibility for the success of the event with the students and that they are responsible for their learning success.