A delay necessary to get mail delivered (4,3)

I believe the answer is:

time lag

I'm a little stuck... Click here to teach me more about this clue!

'a delay' is the definition.
(a time lag is a delay)

'necessary to get mail delivered' is the wordplay.
'get mail' can be anagrammed to 'TIME-LAG'.
However, I am not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for time lag that I've seen before include "Gap between linked events" , "Delay" , "interval" .)

I've seen this clue in The Globe and Mail.

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