Hello.
I know I'm not the first to have this problem, on which I spent hours ...
My contact addon on SPPB doesn't send any email, with any email address used as recipient or sender ("From"). No confirmation message neither.
The email test in the Joomla config (Phpmail) works, and the basic contact form of Joomla works also.
See screenshot of the parameters.
Joomla 4.3.1 / SPPB 4.0.10