Mass mailer doesn't work anymore

Dear support,
Selecting all the users and using the mass mailer fuction, it doesn't work.
I did some test in simulation mode and everything works properly. When i send without simulation it doesn't work.
With PHP 7.3 version appear a message gateway timeout. With PHP 7.2 the process start but still freeze until appair a message: impossible to send email. Only some users receive the email sent.

The CB version is 2.4.6
PHP 7.2.31-1+0~20200514.41+debian9~1.gbpe2a56b
Joomla! 3.9.20 Stable [ Amani ] 14-July-2020 15:00 GMT

Many thanks for your help.
Luca

You're trying to email more users than your server can handle at once. Try using the batch feature so you only email a few at a time or select batches of users to email only a few at a time.

Dear Kyle,
I did as you suggest but i also deactivate the joomla Editor. For the moment with 20 address and 30 second it works properly.
I'll do other test with editor acivated and with more emails per time. I'll request to my internet provider more performance.

Many thanks for your support.
Luca

Shouldn't have anything to do with the WYSIWYG editor, but just that you were trying to email too many at once. The batching will completely eliminate that problem. If you need to regularly email large amounts of users I recommend using a newsletter extension or 3rd party mailer solution like MailChimp to offload the emailing from your web server. Contacting your internet provider won't help with this as they're not responsible for hosting your website and all your web host could do is throw more hardware at it increasing your hosting costs just so you can do larger batches.

Dear kyle,
You are right, thanks for your suggestion.
Leaving the default value (50 email address and 30 second delay) it doesn't work.
I have to send usually to 285 users a email approx 1 time/week. So, also if it takes 7 minutes to do the job with 20 email every 30 second it doesn't matter.

In any case i'll check the solutions you suggest.
Many thanks
Regards
Luca

I have to send usually to 285 users a email approx 1 time/week. So, also if it takes 7 minutes to do the job with 20 email every 30 second it doesn't matter.

That's too regular to be using mass mailer for that task. A newsletter extension like AcyMailing or external solutions like MailChimp would be able to better handle regular mailings like that. This would also let you better schedule the emails so it doesn't require you to sit there with your browser window open as it goes through the batching.