Crossword Genius

What’s left over after sending off a memo? (8)

Ross

I believe the answer is:

reminder

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

'a memo?' is the definition.
(I've seen this in another clue)

'what's left over after sending off' is the wordplay.
I cannot quite see how this works, but
'over' could be 're' and 're' is found in the answer.
The remaining letters 'minder' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for reminder that I've seen before include "Prompt, memory jog" , "Aide-memoire" , "Memory refresher" , "Memento" , "Aide-mmoire" .)

I've seen this clue in The Sunday Times.
Want a hint initially instead of a full solution? Install my app