Sam, with regard to past clients and to some degree with gaining new, I would call personally. I am finding that person to person conversations that demonstrate firstly care and secondly empathy are being very well received in this current environment.
Your clients may feel a little cut off and a voice at the end of the phone might be very welcome. Additionally people have a little more time on their hands and your message maybe well received.
I am currently making personal calls to all my affected employees and its helping us both, So possibly the unusual circumstances require an old fashioned approach.