The most common and most likely answer to this crossword clue is the 7 letter word WEBMAIL
I've seen this crossword clue in Independent
W
E
B
M
A
I
L
Buddy explains!
The straight part
We know that "IT post (as opposed to snail mail)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it post (as opposed to snail mail) = webmail.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WEBMAIL mean?
WEBMAIL noun- A service for sending, receiving, and/or storing email, usually on a remote web server, in such a way that it is accessible through a web browser.
- The email thus stored.