We are glad to see your mail and agree to be there for the discussion.
You could refine it as follows:
In British English it would be more normal to say "We were pleased to receive your invition and agree to be there for the discussion".
What's the difference? You'd be "glad" because something good had happened: "Glad you're feeling better...". "I'm so glad that the flowers arrived in time...". You'd be "pleased" in the same way that you might say "Thank you for your invitation...".