E-mail not sent, test e-mail returns an error

[Mornagest]

Hi Snakes1100 and thank you for your answer

The SMTP protocol is disabled in vBulletin options.

We have a dedicated server.

tail found nothing. We use exim4 and its log looks like this :

2020-11-22 19:27:45 1kgu5Q-0004rB-AR <= EdwardHarrisczoir@iconpln.net.id H=(132.42.202.160.iconpln.net.id) [XXX] P=esmtp S=5550 id=1FDF493F.C830B142@iconpln.net.id
2020-11-22 19:27:45 1kgu5Q-0004rB-AR => administration <administration@mysite> R=local_user T=mail_spool
2020-11-22 19:27:45 1kgu5Q-0004rB-AR Completed
2020-11-22 19:28:04 no host name found for IP address XXX
2020-11-22 19:28:04 SMTP protocol error in "AUTH LOGIN" H=(User) [141.98.10.192] AUTH command used when not advertised
2020-11-22 19:29:20 no host name found for IP address XXX
2020-11-22 19:29:20 SMTP protocol error in "AUTH LOGIN" H=(User) [141.98.10.136] AUTH command used when not advertised
2020-11-22 19:39:31 no host name found for IP address XXX

[...]

2020-11-22 19:53:30 Start queue run: pid=19272
2020-11-22 19:53:30 End queue run: pid=19272

[...]

I skipped many lines that look like those ones.

I have no mail in queue as shown in main admin screen on vBulletin.

So I do not know where the problem lies...

Thank you for your help!