I'm delighted you have accepted our invitation to speak at the Conference in [city] on [date].
As we agreed, you'll be speaking on the topic "" from [time] to [time]. There will be an additional minutes for questions.
Would you please tell me what kind of audio-visual equipment you'll need. If you could let me know your specific requirements by [date], I'll have plenty of time to make sure that the hotel provides you with what you need.
Thank you again for agreeing to speak. I look forward to hearing from you.
Thank you for your letter of [date]. I'm glad that you are also going to [place] next month. It would be a great pleasure to meet you at the [exhibition/trade fair].
Our company is having a reception at [hotel] on the evening of [date] and I would be very pleased if you could attend.
I look forward to hearing from you soon.
[organization] would very much like to have someone from your company speak at our conference on [topic].
As you may be aware, the mission of our association is to promote . Many of our members are interested in the achievements your company has made in .
Enclosed is our preliminary schedule for the conference which will be reviewed in weeks. I'll call you [date] to see who from your company would be willing to speak to us. I can assure you that we'll make everything convenient to the speaker.