Why is only the first email sent after a VPS reboot?

Question

System administration

Good day.
There is a VPS on Ubuntu + Vesta CP. Problem: mail is not sent from the server. More precisely: we reboot the server - I execute a test script - the letter will be sent. I execute the script again, the mail function returns true, a mark about the letter appears in the mail logs on the server, but the letter does not arrive. I will reboot VPS - again one application is sent. The rest don't come. How to win it?

Settings in php.ini:

[mail function]
SMTP = localhost
smtp_port = 25
mail.log = /home/admin/mail.log
sendmail_path =  /usr/sbin/sendmail -t -i
mail.add_x_header = Off

mail logs:

[26-Feb-2020 17:27:00 Europe/Moscow] mail() on [/home/admin/web/site.ru/public_html/test.php:2]: To: [email protected] -- Headers:  -- Subject: Test message
[26-Feb-2020 17:27:28 Europe/Moscow] mail() on [/home/admin/web/site.ru/public_html/test.php:2]: To: [email protected] -- Headers:  -- Subject: Test message
[26-Feb-2020 17:29:39 Europe/Moscow] mail() on [/home/admin/web/site.ru/public_html/bitrix/modules/main/tools.php:6856]: To: [email protected] -- Headers: From: [email protected] BCC: [email protected] Reply-To: [email protected] X-EVENT_NAME: FORM_FILLING_SIMPLE_FORM_6 X-Priority: 3 (Normal) Date: Wed, 26 Feb 2020 17:29:39 +0300 MIME-Version: 1.0 X-MID: 1004.58 (26.02.2020 17:29:19) Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit -- Subject: =?UTF-8?B?aXN0ay1kZXV0ei5ydTog0LfQsNC/0L7Qu9C90LXQvdCwIHdlYi3RhNC+0YDQvNCwIFs2XSDQntCx0YDQsNGC0L3QsNGPINGB0LLRj9C30Ywg0L3QsCDQsdCw0L3QvdC10YDQtQ==?=
[26-Feb-2020 17:33:07 Europe/Moscow] mail() on [/home/admin/web/site.ru/public_html/test.php:2]: To: [email protected] -- Headers:  -- Subject: Test message

17:27:00 arrived.
17:27:28 did not come
Reload
17:29:39 came
17:33:07 did not come ADDITION

: the letters still came after 7 hours. Now I can't figure out why it took so long

Answer 1

/var/log/maillog and other mailer logs. what is there?