hi, I want to send e-mails to my all users, but there is e problem because I cannot send message if there is more than 10 users at once.

in xoops core there is more than 20 users to send at once how to change it to 10 users at once

You have to be careful because most hosts will red flag your account if you send too many emails at a time. Spammers are known to take over mail servers and send out hundreds of emails at a time so most hosts now have a watchdog process that looks for excessive emails being sent out. Some systems get around this by sending mail out in small batches.

I don't see a setting under xoops for this. You may have to address this with your host. I am sure someone has a hack for this but this is likely your host trying to prevent mass emails but 10 emails seems a bit low.

You could use a newsletter module, a module like this sends newsletters in batches I believe...