Ending the newsletter at the end of a sentance will require that your script knows what that looks like ie. will the writer always make sure to put a period, question mark etc. at a sentance end and what about abbreviations like the etc. earlier in this paragraph.

You will also have to decide whether you want less than 2000 or just more than 2000 characters so you can end at the end of a sentance. Getting exactly 2000 seems unlikely. If you cut on words, you may be able to get within 20 or so of 2000 characters.

It may be handier to end at a paragraph and have the writer put in a double newline to end paragraphs. This would be easy for a program to find and could break out if the character count is > 2000 and at the end of a paragraph. Or you could have the author to put 2 spaces after sentances and no where else ever. That could be found and split on.

Basically, you have 2 conditions to end. After a 'sentance' and after 2000 characters. For the characters, keep a running count and determining a good breaking point in software is discussed in the preceding paragraphs.