1) 请对方来发表一个speech，这封信是要感谢对方，同时确认对方对技术设备的具体要求。
Dear Sir/Madam,
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 some time 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.
Sincerely yours,
[name]
[title]
2) 这封信则是请对方来参加自己公司的'一个招待会。
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]
3) 这封信是邀请对方公司派人来做介绍。
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]
4) 邀请收信人参加自己公司的产品演示会。