Will FeedBlitz send old posts if I edit them?

Not usually, no. There is typically enough information in an RSS feed to prevent older articles from being remailed if you edit them.

If you find that edits are being remailed then it may be that you are using an old RSS format (RSS 0.9x) which is archaic and lacks time stamp information. Go to Newsletters | Diagnostics | Diagnostics – if date information is missing then try using a different feed format. Your web designer, blog host support or FeedBlitz support may be able to help you with that. Update your article source at Newsletters | Settings | Content Settings | The Basics with the new feed URL and then go back to diagnostics to see whether date information appears. If it does your emailings should stop, assuming that the dates themselves are correct.