I am a workmate/colleague of Alice, glad to meet you.
一般指“同事”,用 workmate 比较好一点.
补充：按照以上的写就可以了.
或者写 Glad/Nice knowing you.
Glad to write to you.
等等都是可以的,只要在信中把您的意思表达出来就可以了,这也是语言的第一功能----交流.