It is usual convention in initial emails (particularly technical) to expand abbreviations, this way:

We are planning to use the Java API for Registry (JAXR).
After mentioning the expanded form once, subsequently you can use the abbreviation.

__________________
Shaalini.S
Be the Best of Whatever you are...

Make sure you always have a subject in your emails and that the subject is relevant.

Do not use a subject line such as HI.

__________________
Shaalini.S
Be the Best of Whatever you are...

Avoid using "Back" instead of "Back" Use "ago". Back is the worst word for American. (for Days use "Ago", for hours use "before")

Avoid using "but" instead of "But" Use "However".

Avoid using "Yesterday" hereafter use "Last day".

Avoid using "Tomorrow" hereafter use "Next day".

__________________
Shaalini.S
Be the Best of Whatever you are...

"last day" instead of "yesterday".....???? in what possible context?
eg. we were expecting your reply yesterday..............how on earth can you use "last day" in that context? your suggestions are far too vague. How you use a particular word or phrase depends totally upon the context of the message you want to transmit. the 1st two suggestions perhaps but the last two? come on :P