When dealing with people from other countries via email, make sure you spell dates out in full.
Instead of putting 1/21 or 12/5 why not put 21st January or 5th December? Or in the case of the second one it could be 12th May, depending on who wrote it and where they live.
In some countries the day is written first and the month second, and in others the month first and then the day.
If dates are important in the communication don’t assume that the recipient is on the same page as you with respect to writing dates. Write them out in full to save confusion and incorrect information being conveyed.