PHP mail stopped sending. Where to look?

Question

PHP

After installing mpm-ITK to run Apache on behalf of the user,
mail stopped leaving php mail ()
Debian 8 system instead of sendmail'a exim

Answer 1

In general, he asked himself, answered himself.

# to send PhpMailer mail via Exim and SSL/TLS
LimitUIDRange 0 6000
LimitGIDRange 0 6000

add here: /etc/apache2/mods-available/mpm_prefork.conf