Which database engine do i have to choose for more than 300 users login

[ste74]

Hi Forum ,

I have my web email site keep growing month by month .
I started using sqlite3 but now i think is the bottleneck.

It happen when i have an high loging concurrency eveyting become slow .also i already tuned php-fpm,os tcp / ip stack .

But i think to solve swithcing to mysql because sqlite3 when write is single thread.


Someone help me ty