This is the one time you should ignore your supporters. Because thanking them is probably the best investment you'll ever make. Particularly as now, more than ever, giving to charity is incredibly generous of people who are wondering if they'll be able to afford to pay for their groceries next month.

We recently wrote a thank-you letter for our client RSPCA. But it wasn't just any old thank-you letter. This letter thanked donors for everything they'd done for the charity during the previous 12 months. Every response to an appeal, every raffle ticket bought was acknowledged. And thanked.

There was no ask for money in this letter, yet the volume of 'white mail' it generated was far in excess of any RSPCA fundraising appeal (10 inches high and counting…). And none of these letters said "Don't waste money thanking me".

Many supporters wrote and phoned saying how they hate being asked by charities to give more all the time, then going on to say that because of the letter, they'll increase their gift. Another was prompted to leave a residuary gift in their Will.

Being the hardcore direct marketers we are, we wanted our client Sarah Vickery to test it so we could see how it affected the future 'performance' of the supporters who received it. Now Sarah understands DM as well as we do – but she said "No!" And do you know what? I think she was right, because Sarah recognised that there are some things that are so right to do that you don't test them – you just do it!

Nick Couldry