No notification sound in outgoing mail

[1di9]

On my Oneplus 5t with Android 10 I've set a notification sound that should be played when sending an email but this sound is never palyed when I send an email. No problem, instead, with sound for incomig email.
I'm using aquamail with identical settings on other device  (tablet Asus Zenpad 3S 10) with Android 7 and notification sound in outgoing email is played correctly.
Is there any solution?

[JosieQ]

Same problem, Android 9 on Xiaomi Redmi Note 8. (MIUI Global 11.0.9)

Send notifications set for ALL accounts, and when that didn't work I went in and set them individually with "special settings" for each account, still no sound. :/

Incoming individual sounds working fine for me too, luckily.