Possible Clues:

• No more mail of late - blow it!
• Final job for an army bugler
• Bugle call for sunset or funeral
• British taps
• That's the final Evening Mail on the blower
• It sounds as if there's no more mail after 18 down
• Bedtime bugle call
• Military bugle call at funerals and sunset
• By the sound of it, it's something one might find in 32 across
• Bugle call sounded at sunset