I was a reader for the Inkwell Festival last year, and to celebrate finally completing the first round of reading 500+ plays (!), they forwarded us some of the thank-you notes they got from playwrights.
These thank-you notes were wonderful: gracious and appreciative. The playwrights thanked the Inkwell for considering their play, for all of the feedback (the readers made comments on all of the plays), and for other things they were grateful for.
That’s the way to write a thank-you note. Because that kind of thank-you note will get you remembered favorably by a reader, or literary manager, or an artistic director. I guarantee you I will remember those playwrights more favorably than anyone who would respond with complaints –about how long it took the theater to get back to them, about the comments they got, anything.
Graciousness and generosity are good traits to cultivate, in life as well as in the theater.