[Grammar] Preposition ‘in’ vs ‘after’

[northpath]

Why two different prepositions?
This message is marked as junk and will be deleted AFTER 10 days.
John will be back IN 10 days.

 

[emsr2d2]

Both are acceptable in the first. It could have said "will be deleted in 10 days" although some people will argue that means it will be deleted on day 10, whereas "after 10 days" means on day 11.

The second is much more natural with "in".