Ironically, your error message contains no error message. :rolleyes:
Check your IPB's sql logs for more info.

I would assume, you may have hit some sort of sql limit.

IPB SQL logs (are more so):

???

Possibly...
1. Your mysql server crashed.
2. You reached mysql limits. Check from mysqltuner, it'll also tell you if it reached its limits (most likely)
3. You may have reached tcp connection limit (not very likely)

1. Is not crashed mysql server
2. I ran mysqltuner but do not see any warning in this respect. So, they stopped sending emails to 450. I tried three times to run resending emails and each time the block to 450 emails. It just does not want to send more.
3. How I can check tcp connection limit ?

are you using php mail or smtp?

I typed the command 'top' and the list shown not see anything about php mail or smtp! I see only command sendmail or user smmsp.

how is your board set for mail.
php or smtp?

if php try setting up smtp, wondering if (with that many emails) you are hitting maxexecution or tcp limit.

php mail

and I don't think is the tcp limit ... or I don't know what to think ... however, something don't leaves IPB board task Bulk mail to send over 450 emails, but who is this "something"?

setup smtp and try that.
depending on size of msg may be hitting resource issue in php.
you may have to allow the smtp user to send that many, thats mail server setting.

php mail, iirc, opens a seperate tcp connection for every mail sent.
which is why real mail servers don't use php for mailing.

I try setup smtp but don't work. I don't think so is smtp or php mail, because I can send 450 emails. So I think that is a limit imposed by the mail server, that has nothing else to be.

How I can check mail server settings ?

what errors did smtp give?

Don't give errors smtp - simply does not work.

But, again, the problem isn't php, because e-mails are sent but can not send more 450 and do not know why!

so you know the issue is not php w/o knowing what the issue after being told php will not work for mass emails like this?
have fun.