One more thing: chances are the director's inbox is handled by their PA, whose job is to filter out things the director doesn't need to see.
If the PA thinks the director will appreciate the thanks, they'll pass it on. If not, they won't, and no harm is done. So, chances are the director will only see your message if the person who knows them best in the organisation thinks they'll be pleased to see it.
The PA will definitely see it, however, and they might remember you as someone courteous. This is no bad thing. In my experience, PAs:
- Tend to really appreciate good manners (since it's an important part of their job, and because they're often on the receiving end of bad manners from self-important people they have to be nice to)
- Tend to be remarkably good at remembering who everyone is
- Tend to be very useful people to know - they sometimes seem to be about the only people in the organisation who truly know how all the organisation's processes work and what is going on at all levels of the organisation
- Are important to get on well with if you're ambitious, since if you do ever need the director for anything, they'll be the ones making the call as to whether you can be trusted with the director's time
Keep it short and sweet - you don't want to waste the PA's time, either.
A very good tip for emails like this is to include all the main content concisely in the subject line, in such a way that it's obvious from the subject line alone that this is a polite email that doesn't need a response.
All the directors' PAs I've known have really appreciated little things like this. They're usually juggling at least 5 things at once, and it's the difference between seeing an email popup and thinking "Oh, that's nice, I don't need to do anything now but [director] will like that, I'll skim it later and mention it in our 2pm catchup", vs thinking of "Huh, what's this about, I'd better read it... Oh, that wasn't important".
So, for example, a subject line like "Thank you for providing us seats at [event]".
Snappy, simple, and they'll know immediately what (if anything) to do with it.