Dear Sir/Madam，
[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 promotion. Many of our members are interested in the achievements your company has made.
Enclosed is our preliminary schedule for the conference that will be reviewed in the coming 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 as convenient as possible for the speaker.
Sincerely yours，
[name]
[title]
Dear Sir/Madam，
On [date]， we will host an evening of celebration in honor of the retirement of [name]， President of [company]. You are cordially invited to attend the celebration at [hotel]， [location]， on [date] from [time] to [time].
[name] has been the President of [company] since [year]. During this period， [company] expanded its business greatly. Now it's our opportunity to thank him for his years of exemplary leadership and wish him well for a happy retirement. Please join us in saying good-bye to [name].
See you on [date].
Yours sincerely
[name]
[title]
Dear Sir/Madam，
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.
Yours sincerely，
[name]
[title]