Regrets deposit involved in a safety procedure (10,4)

I believe the answer is:

registered post

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

'a safety procedure' is the definition.
The definition suggests a singular noun which matches the answer.

'regrets deposit involved' is the wordplay.
'involved' is an anagram indicator (involved can mean confusing or complex).
'regrets'+'deposit'='regretsdeposit'
'regretsdeposit' is an anagram of 'REGISTERED POST'.

'in' is the link.

Can you help me to learn more?

(Other definitions for registered post that I've seen before include "sign for this?" , "Special form of delivery" , "Specially secure delivery" , "important letters? - with 28a" , "Type of mail" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.