Sometimes there are intermittent connection problems between email providers. They can be due to network issues, mail server problems, blacklistings, etc. How long has it been since you sent the four emails? Did the problem already resolve itself? Did you get any bounce messages? If not, did your friend in Russia check their spam and other folders for email that was filtered into the wrong folder? Can they can an email from you if you send it from another account such as a Gmail or Hotmail account?